The thing is...combat in DOS2 is fun, combat in BG3 right now is frustrating and kind of boring (1 action, 1 meeeeh bonus, move).
PnP D&D works because of the human element (DM). So Larian need to spice things up. Add some unique mechanic to counterbalance that cold, by the numbers computer DM. Maybe a DM bar/button which fills up as you battle (maybe because of too many critical misses, bad rolls, being slaughtered etc....), giving you bonuses or extra fun light rule braking abilities..."as the goblin lunges towards you for the killing blow, he slips on comrades corpses blood and impales himself..." kind of stuff. Basically a D100 of fun "larian touch" effects that can happen

Well - whether combat in DOS2 is fun is a matter of taste/perspective. To some it is very fun and enjoyable. I tried to play 20+ hours of both DOS1 and DOS2 before I gave up because I did not enjoy their combat systems, it was just wacky and cheesy and annoying to me. And I get the sense I am not alone.
Combat in BG3 could be fun, but the annoying surfaces and jump disengage are mechanics that take the fun away from me. If some bugs were fixed and those things were reduced/fixed, then I think I'd actually really enjoy combat in BG3.
The turn-based mode for Pillars of Eternity Deadfire is also a good inspiration that could be used.
I think the game/Larian needs to figure out if it wants to give DnD5e a serious chance (with some adaptations/changes where necessary) and make what they promised in most of the advertisements. Or if they want to make another Divinity game. The weird hybrid is not working for me at all. I am sure both could be good games - I know I won't enjoy it if they choose the Divinity path, but many others will. And I'm sure some won't enjoy it if they choose the DnD5e path, but then many others will. The hybrid seems to just make most of the people from both sides of that "divide" annoyed.