I agree with OP about excessive advantage and implictaions. I redid one combat were I started with height advantage, and it was vastly easier. Also, the AI always scrambles to get all your opponents on to high ground, precisely because advantage is such a huge deal in 5E. I also think backstab/sneak attack should work as intended - they already have a threatened status so the data is all there. The term 'backstab' was dropped from D&D ages ago, because well, you didn't need to literally 'stab someone in the back' ;-) It really is a defining rogue feature and should be triggered more easily (as per 5e rules) - that was by design. I really hope Larian take this feedback on board - I am happy to see that cantrips no longer create elemental surfaces.