The biggest problem is that they apparently lied about implementation. For real, if they had implemented 5e mechanics RAW in the EA and feedback was overwhelmingly negative, though I'd probably be on side of the few that would've liked it (based on Solasta), I'd understand if they changed it to be more like DOS based on a sales strategy. Games have to make money, I get it, no one wants this to fail.

However there is no evidence that they implemented RAW mechanics at all, but there is evidence that a mostly faithful adaptation works well, in fact, Solasta is getting higher scores than BG3 on GoG.