the only way to more or less enjoy BG3 is to mess around with builds
If only. Experimenting with builds is pretty limited. Everything is too tailored and straightforward. That’s my main gripe with 5e.
Well, the multiclassing options are actually rather decent, if not on Pathfinder or Deadfire level.
Problem is that you typically need somewhere around level 8-11 for a multiclass build to mature. And the prospect of needing to reach the late Act 2 / Act 3 again in order to just play around with a new build is, well... ugh...
By the time you make any "interesting" build work, you got so many broken items that just going 10-12 levels into a single class will feel basically the same. At the end of the day, most of the builds will just use the same few gimmicks of either stacking too many damage riders or using one of the status effect mechanics, like radiant orbs, reverberation or the bullshit that is arcane acuity - making your class choices large inconsequential.
Also on the topic of reactivity - it's just an illusion. Any path that branches of eventually goes back to the same main road. And a lot of the choices are actually just: be good and get good loot or be bad and get a bad story with bad loot and eventually go to the same boss fight regardless of your choices. Want to spend the game resisting the "guardians" influence and never use a single parasite? Go ahead, you're still getting forced into the narrative that you used all of them and now are ready for the next step of the transformation. Tell the guardian to fuck off every 5 seconds, never trusting him etc. - well well well, what a perfect segue for a sex scene with a fucking octopus.
The game did a great job providing a decent low level DnD experience, having a very polished act 1, where the choices made kinda seem like the game is reactive while in the context of act 1. For the average gamer who preorders slop like Veilguard, the beginning of this game was enough to convince them that it was GOTY (and maybe it was, not like the market is full of any decent games anyway.) But for any gamer who has half a brain and has spent years playing RPG games, this game becomes a joke once you get more than 8 magic items by level 4, while the game never actually provides enough of a challenge to throw so much broken shit at the player.