Let's do another scenario to illustrate the difference between Level 1 and Level 6:

5e. Life Cleric, Fighter, Mage, Rogue versus 4 phase spiders.

Round 1 - Phase spider wins initiative. Ethereal Jaunt. Unseen in Ethereal Plane - Like invisible only more effective - it moves closer to party using Dash so it can go 60 feet. Mage is next. Geez. Phase spiders are 180 feet away. Out of range. Still, he casts Misty Step, moving 30 feet closer, and moves 30 more feet so he can get closer so next round he can cast Fireball - hopefully. Fighter is next. She moves 30 and uses longbow... because it has range of 150. She shoots and hits Phase Spider 2. Uses Menacing Attack. Does 8 damage (1d8 for longbow and 1d8 for Menacing Attack +2). Phase spider resists fear. Fires again and misses (gets 2nd attack because at level 5 fighters get another attack). Rogue is next. Moves 30 and drops into hiding behind a rock. Can't hit with shortbow (assuming since it's a video game that we'll stick with main ranged weapon ranges as opposed to extended Disadvantage applies ranges). He readies a Ranged Attack (hoping they add Readying actions like Solasta has so that if an enemy moves within range he gets to use his reaction to attack automatically. This isn't hard, guys. Xcom has Overwatch. It'd be not much different). Phase Spider 2 goes. Ethereal Jaunt. Phase 3 goes. Ethereal Jaunt. Cleric goes. Moves 30 and casts Bless on himself, Fighter and Rogue. Phase 4 Ethereal Jaunt. So, after 1 round, very minor damage done to spiders. No damage to party. Let's just stop combat there and compare to BG3.

BG3.
Round 1 - Phase spider wins initiative. Ethereal Jaunt across board to be right on top of characters. Spits on everyone in the party with poison and does 6 to Fighter, 10 to Cleric, 12 to Rogue and 11 to Mage. Mage is next. Misty Step 30 feet and moves another 30 to get into range. Casts Fireball on 3 remaining phase spiders. Ew. Only rolls 16. Kinda low damage for Fireball. Two phase spiders, however, fail the save. So 16 off each. Half dead in one hit. One succeeds and only loses 8. Quarter dead. Fighter is next. She just uses her Everburn Blade at close range with Phase spider 1 and Menacing Attack. First attack hits. Second misses. Deals 21 damage (2d6+1d4 fire+1d8 Menacing Attack). Reduces Phase 1 to 11 HP. Rogue is next. Moves up to Phase 1 and attacks with main hand. Misses. Attacks with off hand with Sneak Attack and hits with shortsword. 4d6+4 damage (he has 18 dex). 19 damage. Phase 1 is dead. Has Fast Hands. Moves into hiding because has another Bonus action. Phase Spider 2 goes. Ethereal Jaunt across board onto Mage. Attacks. Hits. 1d10+2+4d8 damage (resist with DC 11 Con). Rolls 8+17 poison. Mage resists and takes half, so 16 HP lost. Mage has 23 remaining. Phase 3 goes. Ethereal Jaunt onto Mage. Attacks. Hits. Mage fails to resist. 24 damage. Mage is down. ("Well, THAT sucks," says the Mage player. "I was 120 feet away and they ported right on me and took me down. At least I got a Fireball in.") Cleric goes. ("Don't worry, Mage. I'll get you back up.") Moves 30 feet. Throws Superior Potion. Heals 14 HP. Mage is back up. Casts Healing Word at Level 3. 3d4+5 healing. 11 more HP. Mage is back up to 25 HP. ("Kiss my butt, phase spiders.") Well, no Bless for you, Fighter and Rogue, Mr. Cleric. You spent your round boosting Mage's health to 25 HP. Phase 4 Ethereal Jaunt right on top of Mage. Hits. 12 HP off. Pshew. Mage got lucky. Phase 4 rolled low and he resisted the poison. 13 HP remaining.

So, after 1 round, major damage done to both sides. Very volatile. Mage was taken down and brought back up (which, by the way, negates one of the phase spiders' poison traits which states that once you reach 0 HP, you are poisoned but stable for 1 hour, even after regaining hit points, and would therefore be paralyzed while poisoned in this way. Meaning, the Cleric would not only have to run up and heal the Mage, but he'd also have to use Lesser Restoration to get him back into the action. Ah! What? A use for Lesser Restoration? No! Say it ain't so. Well, that would certainly make the cleric that much more vital, wouldn't it?) Anyway. All 4 phase spiders are more than half dead in a single round, and one IS dead. And what, exactly, were the strats used? Fighter. Move and attack twice with Menacing Attack. OK. Not exactly big strats, but neither is moving and shooting a bow twice. So, not much different. Rogue. Move and attack twice with melee. So, pretty much the same as fighter. No drop into hiding. No readying an attack in case a phase spider appears. Just move and attack twice. I suppose he could have done something different, but why would he? Phase Spider is right there. Run up and hit twice, at least hitting once with Sneak Attack. Mage. Misty Step and Fireball. Well, now that's major. Talk about an OP strat. Now 3 out of the 4 spiders are half dead. Cleric? Poor Cleric. The super volatile nature of the game allowed 2 phase spiders to pounce on the mage and take him down. Time to bring him back online. Hurl a potion and cast a spell and he's gone from 0 to 25 HP. This prevents him from being dropped when the 3rd phase spider pounces on him.

Now let's see how round 2 goes:

5e. Phase 1 is still alive in the Ethereal Plane. He moves another 60 feet towards party. Mage gets nervous. He knows that they are likely moving at 60 feet per round. So, he can calculate that Phase 1 has likely moved 120 feet. That means that he's still in an okay position for one more round, but the spiders will likely pounce on him next turn. No matter. Let them come. This gives him a round to cast Mirror Image. Now they'll have a MUCH harder time to hit him with DC 12. According to 5e rules, even if they hit, he gets to roll a d20. With 3 duplicates, he only needs a 6 or higher to transfer the attack onto one of his duplicates. That's a pretty significant chance. With 2 Duplicates, if he rolls an 8 or higher, the attack strikes a duplicate. With 1, the attack strikes a duplicate at 11 or higher. So, it's like he has minions that he can transfer the attack to, and each minion gets an AC of their own (10+Dex, so in this case 12). But even, let's say, we use Larian's simplified version. Each enemy gets a Disadvantage to hit him until all three of the duplicates are destroyed. Still a rather good chance that he will avoid getting hit. Mage is basically using himself as bait to lure out the spiders and buffing his defenses while doing so. ("Come to me, my pretties.") Fighter is next. Moves 30 feet and readies a ranged attack with the longbow. Rogue remains in hiding. Readies an attack with shortbow. Phase spiders move. Cleric moves 30 feet towards mage. Casts Spiritual Weapon and places it near the Mage. Makes it look like a hammer. Last phase spider moves. Quick round, actually. Most didn't do much, but they were preparing, strategically, for when the phase spiders will appear.

Round 3 - Phase 1 runs 60 feet up and is now in range. Waits. Mage casts Mage Armor, adding 3 to his AC, going from 12 to 15. Ah! Much harder to hit. Again, "Let them come." Fighter is next. Moves up to Mage. Switches to sword. Readies an attack. Rogue again readies an attack. Rest of the spiders move. Cleric joins Fighter and Mage. Readies an attack. Last phase spider moves.

Round 4 - Phase 1 Ethereal Jaunts and returns to the material plane. Fighter, Rogue and Cleric readied action triggered. Whoa! I just rolled it. 2 Nat 20s and a 19 total. 3 hits. Fighter deals 15 damage (2d8+2 with Crit). Rogue deals 13 (2d6+4 with Crit). Cleric deals 4 (1d6+2 without Crit). Total damage done to phase spider is 32. Killed Phase 1. Why? Strats. Reaction expended for all 3. Mage's turn. Hmmm. That was pretty effective. Should he change strat? Chances are, the spiders will come up to the Cleric and Fighter now if he falls back. However, he just buffed his defense pretty good. What if, instead of using Fireball, like he was planning, he uses Thunderwave Not as much damage, but the last 3 spiders would likely pop up on them right next to one another another, lining up with the Cleric, Fighter and Mage who are in a line. He could hit them all with one spell. Ah, but if he readies the Thunderwave, the first phase spider that appears will be the one to trigger it, so he would not hit them all, just the one who appeared. He might want to use a spell that would be more solo-enemy based. Well, he considers Fire Bolt because at level 6 it deals 2d10 damage. So, why not? Oh. Wait. When it appears, it will be in melee range. He'll get Disadvantage to hit because it's on top of him. Shocking Grasp it is. That's fine. It does 2d8 at level 6. That's pretty good. So, he is about to ready Shocking Grasp. Fighter readies attack. Rogue hides again with Expertise and succeeds. Readies an attack. (But, you might say, how can they do that? They already used their Reaction, right? Nope. They used LAST round's Reaction. As long as they use their Readied Action before their next turn, it is the previous round's Reaction that is used, not the current round's. Phase Spider 2 appears. Wizard uses Shocking Grasp, Fighter attacks with sword. Rogue fires bow. Mage hits with a 20 total. Fighter misses with a 9 total. Rogue hits with a 22 total. Mage does 8 damage. Rogue does 7. Good strats, but definitely not as lucky this time. Only 15 off because no one got a crit while previously 2 people got crits. So, phase spider is down to 17 HP. Phase 2 now attacks Mage. Rolls 15 total and hits. BUT, Mage rolls a 14 and transfers the attack onto one of his duplicates. Duplicate disappears. Phase 3 appears. All readied actions are finished. Phase 3 attacks mage. Hits. Mage rolls an 8 and transfers the attack to a second duplicate. Duplicate disappears. Cleric's turn. Hmmm. His most powerful attack is Guiding Bolt, but now he's at melee range. The most he can do with his mace is 1d6+2. He DOES have an area effect spell - Word of Radiance. Yes! That'll work. He casts Word of Radiance (a cantrip spell I'm hoping they add soon). Deals 2d6 damage to each creature of his choice that he can see within 5 feet. So before casting it, he dances around one of the spiders and lines himself up so both spiders are next to him. If they fail a Con roll, they receive damage. If they succeed, they don't get hurt at all. Dang! Both succeed. No damage. No matter, Spiritual Weapon can be moved and attack as a Bonus action. It swings and hits. 1d8+5 damage for a total of 7. Not bad. Now it's lost 22 HP in a single round thanks to what? STRATS! Phase 2 only has 10 HP left. Phase 4 finally gets to go. Rushes around and attacks Cleric because he's closest. Critical Miss. Better luck next time.

So, after 3 more rounds, 1 Phase Spider is dead. 1 is down to 10 HP, but the rest are full health. Various party members used various strats to get to this point, and not a single party member is hurt. Will they need a Long Rest after this fight? Probably not. They've used some spell slots, but nothing major. Short rest would probably do it. Shoot! The cleric probably didn't even need to use any. He just chose to because that was the strat he was using.

Let's see how BG3 would do.

Round 2. Phase 1 is dead. Mage Misty Step away from the 3 Phase Spiders. Fireball... because, why not? You can long rest after and get all your spell slots back. Rolls 30 damage from 8d6. DC is 14 for this wizard. Rolls are 14, 20 and 3. So, half damage to Phase 2 and 3, but 4 takes full. Half damage is 15. Full is 31. Wait. How many did they all have to begin with? 32 HP. So, Phase 2 and 3 only have 1 HP. Phase 4 is dead. Fighter's turn. Fires longbow. Hits. Phase 2 is dead. Fires using 2nd attack. Hits. Phase 3 is dead.

Great fight! [sarcasm] Lots of fun. Mage did most of the work, and all it took was Cleric to expend a single potion by throwing it. Then he used a single spell slot to cast Healing Word spell. Yeah sure. Mage expended a bunch of spell slots, but is that really a big deal with long rest spamability? No. Just long rest after the fight - wash, rinse and repeat.

Tell me that BG3 won't get boring once you get to level 5 and beyond.