I agree with a lot of the issues you get into and how they don't feel great, but I don't think 5e is the problem. As you said, they could add in little situational bonuses based on previous actions and such and that would fit in totally fine in 5e.

You mention combat isn't as interesting as DoS2 and I think that is a problem, but I think right now they are half DoS and half 5E and if they just went with one or the other then it would be better. I was hyped for BG3 to play a 5E game. I love DoS 1 and 2 and will happily play a DoS3 with DoS based combat, but for BG3 I want faithful 5E combat.