I doubt that Larian really tried. They just used the DOS combat engine with all its quirks and special abilities and added a D20 to it. But the core is not D&D
That’s my impression. They spent the majority of time on their graphics and it shows. The game is beautiful.
5e ruleset is heavily designed on action economy (you can’t do a bunch of things at once without very specific special abilities) and bounded accuracy (to hit bonuses and AC are limited). Those two things must be in check in order to maintain balance in combat otherwise you get what you see in BG3.