Yeah, the UI definitely needs work.
IMO, BG3's UI needs to be even better than Solasta's - because the game / mechanics is going to be more complicated with multiclassing, etc.
I.e. they need to make sure to design it in a way that if I'm a Paladin Battlemaster, it's possible and also easy for me to apply both Divine Smite and my Battle Maneuvers to the same attack.
Honestly, I hope Larian doesn't even try to implement multiclassing. With their level of incompetency, the multiclassing can turn a very mediocre game into a disaster.