4. I both play and DM D&D, I did so in the last 25 years, thank you. As said above in D&D 5th edition damage spells are designed to do more than attacks while attacks are obviously more consistent because they are not limited by spell slots. You either use damage spells to get rid of a single opponent ("save or suck" spells work better in this rergard though) or to weaken/kill minds of weaker enemies. Generally speaking martials don't work that way and can't do those things (paladins can effectively go nova thoiugh... if they spend spell slots!).
If you look at the spells I just pulled from a few of my players, the differences in spells aren't really in damage. I circled the things in purple that are consistently different. Now, Clerics and Warlock (limited spells) are the truest casters in the game. The wizard needs some work. You talk about big damage but the wizards really don't have it because if you are talking % of total enemy health per round relative to a 5e game, they are doing significantly less than your normal caster due to the nature of the encounter. Spiritual weapon, Tashas, Toll the dead, Spike growth, Spare the dying, Absorb elements, SHIELD, and sanctuary are spells that drastically change not only the DPR, but the shutdown for movement (spike growth), and advantage (tashas). This is a difficult conversation to have considering some of the most commonly chosen and used spells are missing from the book. Casters doing damage is nice, but there are other ways to guarantee SOME damage - spiritual weapon and spike growth especially are crazy good to just throw out there and now you have a spell that is pretty much guaranteed to succeed. Things like Tasha's are such a staple because of the prone condition that they have to *continue to save on* (without making an ice patch your own team can eat shit on).
And the point, again, is combined with HP bloat that line of "Take out a single enemy" is no longer an accurate statement.
5. Yes, BG3 resting system doesn't work (imo) as it is now it just makes casters better than they are in D&D because they don't need to manage resources and can always go nova this fact currently makes your claims about spellcasters getting less from spellcasting null & void imo.
Cant sleep in the middle of a 7 round fight, now sure where you are getting Null & Void from.
I completed BG3 EA twice and combat felt just fine if a bit easy. You claim you feel boredom at how combat works... but the current system encourages you to position yourself and to move tactically (which requires a bit ot thought on the player's part) while you ask for the nerfing of opponents so that your spells can do more than they already do (read: a lot) and the removal of those modifiers that make martials better at attacking the enemy while positioning themselves in order to gain those advantages (advantages that btw, work for casters as well as martials, try to cast a cantrip from higher ground than your target, your chances to hit will be better than what you'd have doing the same while on the same level as your opponent). Basically you are saying you are bored because your spells can't kill stuff on the spot (and they actually can, btw) without you needing to position yourself tactically in order to gain advantage/defend yourself from reprisal.
Half the time "tactics" means climbing up a rope or a ladder, burning it so the melee cant get to you and hiding out of LOS and just dumping arrows and firebolts and then dodging out of LOS again until they die. I wouldn't call it particularly clever, its holing up repeatedly so you don't get burned down and you save your spells for when you need it instead of using spells because they might work. The round economy breaks the 3 round fight and spell slot usage because of how long it takes to decrease enemy DPR from HP bloat. So, what do you do, you give as much advantage to martials as you can because they're the ones who are going to consistently hit and do damage. Its way better to empower them than blow 3 2nd level MMs for 12 damage on a creature that has 25hp instead of 10. Now you'll knock them down with ice and let that martial go to town. Thats the economy change that starts coming down the pipe because of the matrix. Again, this game does not play like D&D. You dont use the same spells in the same way for the same reason. You position martials and casters differently than you would. You are playing on a retreating action consistently and its dropping the "5e players are impossibly strong" theme that DMs run into time and time again. 5e favors the player significantly, and this is definitely not.