Ranged 4d6 AOE with poison cloud that last way too many turns. A level 4 spiders shouldn't have that, boss or not. Actually, 5e phase spiders don't even have ranged attacks, they are pure melee.
Also, that boss only give 20 XP, level 3 Goblins gives 25XP. Someone just put that there to see what players would do I think.
That last bit is true to many of the things I've said on other posts, and why game is in EA. Which is a testing ground for a larger group of people. Not sure about the entire dice thing I'll test it out, or do you have a screen shot of how much damage? I personally didn't check, or notice but again I took her down really fast, then focused the mid level. The fact that phase spiders are different in 5e is again probably do to Larian trying it out, and their noteable love for wide spread effects. Nothing really knew there, it's part of what makes them who they are. And the op is about HP bloat. Yet so far only one I've heard of is this spider.
I'll need to do more fighting with her, and make sure it lasts awhile this time, stead of 5 rounds top. Oh poor Larians going to have more information. In my playthrough which currently I've fought her twice she never used the aoe, instead summoned spiderlings, and hulked out.
Is bad in ANY game.
At least make it OPTIONAL!!!!
Eg - "original AC and HP (not recommended)" on settings.
So people who enjoy having to hit an spider with 30 crossbow bolts can enjoy their slow and tedious fights and people who enjoy deadlier encounters can enjoy their fights.
That's not an example of something which could reasonably be an option. HP/AC has to be consistent - at least per difficulty level, otherwise the permutations for balancing become too difficult.
The excessive focus on balance is what is killing modern RPG's, but that is another discussion. The main point of a game is to be fun and entertaining. Balanced or not, seeing all your cool weapons/spells being ineffective against an enemy is not fun IMO.
The HP bloat is problematic, regardless of a lowered AC value. Simply due to the fact that fights, especially the larger ones, take longer and use up more resources than they should. I'm not saying that every goblin must have 7 HP, but neither do they need 15+ HP like some in the Selune temple/Goblin camp. It also devalues spells like sleep that are affected by the HP of the enemies.
So all goblins are supposed to be universal or near universal. Some of those goblins have classes in cleric, fighter what not which is standard in D&D. It increases their toughness, gives them some perks to make them a viable threat, and turns them from common mob to something a bit more dangerous. Also is used to show that they are not run of the mill goblins, but ones who have trained to do something in particular. Like guard the camp, or boss, maybe they have more experience in battle. Have just blah mobs that are easily one shotted is MMO mindset, not D&D. or most rpgs for that matter. Skyrim Bandit Bosses, Bandit archers, Bandit mages all have different hp levels to show their experience and their training. Goblins should not be any different #goblinsarepeople to. Unless of course you want a world filled with trash mobs, and no realism, one that is without the nuances like goblins having different hp, abilities etc as boring as watching paint peel. Which is an MMO thing and why I don't play them.
On to fights taking longer then they should, yes that is a problem it's not do to hp bloat. It's do to numbers of enemies, balance overall, and to many encounters coming at once. Then again all the encounters is part of most video games, were you mostly walk from one fight to the next. It's not hp bloat it's pacing, which since you can simply camp, fast travel isn't all that much of a problem at times. Though it can be. Which leads back to balance, Balance of not only combat, but the world. How do you make a world feel alive with only a small number of npc's in it. more often then not you dont' because it feels empty. So do you spread the map out a bit more. For instance moving Guts further away from main hall, moving the Zhent trader somewhere else, so on and so forth. Then your using more memory up by adding additional areas, which increases load times. So then you have other issues, which through EA can be fixed. One of the Guts fight problems can be fixed by simply having fewer goblins come to her aid, and having the Zhents stay out of it. Why they would really care about this fight, and not bug out is beyond me. Whoever wins they can trade with.