I agree that backsatb shouldn't grant advantage. However, I like that you can get advantage from height, and imo the rules don't have to be followed precisely if the changes that are implemented make sense and are fun to play. Which, I think, applies to height advantage.

In addition, the fights we see in the EA so far all have some degree of verticality, and Larian has stated before that this is on purpose to allow both players and enemies to gain advantage in a battle and therefore make it more tactically interesting.