Honnestly I'm not interrested in BG3 "because it's a D&D game" but trying to learn what I was talking about here lead me to this conclusion : D&D has a stronger, deeper and more consistent system than the hybrid system we have in BG3.
I don't understand why a video game couldn't have a strong, deep and consistent system and a few "fun" homebrewed additions at the same time.
Again, it's only a matter of balance not to drive players in a way more than in another.
That approach would have required Larian to start with 5E rules, and then modify change those rules, but that's not what happened. They started with DOS, and then tried to add in 5E, found it too difficult and/or didn't really understand 5E rules well enough to balance changes to them, and what we have is the current gobbledygook of DOS with a smattering of 5E.
Technically, from what I remember, Swen mentioned that they started out with very strict rules but internal testing showed that they didn't work well. Believe it or not, it doesn't matter.