Welcome to Larian 5e D&D. They've made countless changes that deviate significantly from 5e, and without exception all these changes have drastically influenced the balance of gameplay. Over 45 years of D&D evolution casually tossed aside to make BG3 more similar to Larian's own DoS games. There's over 70 pages of threads talking about these issues. We can only hope, that being an EA game, things will significantly improve before an official title release. We'll see.
First, well stated. The balancing in 5E is pretty precise, and so any seemingly small change can actually have a big and unforseen negative consequence. I am hoping Larian has a 5E pro working with them on this, who really understands why 5E makes the balancing choices it makes, and how changes could cause problems. I really want to like BG3, and there is alot that is good, but regarding its implementation of 5E rules and mechanics, it has a long way to go from where it currently is to get there. I am rooting for Larian to pull it off.