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
Yeah I agree the Core of BG3 just does not get my D&D experience so saying this is D&D 5e is just not telling a whole truth. Mind you I have been playing D&D/AD&D since the 80's and BG3 system just breaks it.
I mean I am thrown back when my fighter in BG3 could use the scrolls and I was like WTF, and the Dip action.. Waaa? The move and Jump bit, everyone can lockpick anything etc etc. It is the simple basic rules of D&D and if those are not used correctly and possible expansions/addon's to BG3 will really really break the game. For those who come from TTRPG and play this will go 'This is not 5e D&D'. Really if BG3 is not really using 5e rules (just a hodgepoge of a system) then do not market it as 5e D&D. Of course I do not know how much of an eye WOTC really is watching about the game (if at all).
Now the game graphics is absolutely beautiful as is the voice, getting the mannerism's etc. I mean this game looks great (as a Alpha version 4 and we know we are all test bunnies) compared to games that are actually released.