Yea so you're litteraly asking not to enjoy any verticality in the game^^
Advantage is not the only thing highground could give as a bonus.
No more advantage for highground = many more viable and balanced possibilities to have an advantage = more tactical decision/choices.
Highground could give other bonuses than advantage : +2 to attack rolls, +2 to AC, better range, with a few adjustment to the maps it could also be a kind of "cover" mechanics (because you can often hide more easily or break the ennemie's lign of sight).
It could still be very interresting without being THE only thing.
What would change is that highround and/or backstab wouldn't probably be enough to have a satisfying %to hit. Players would have meaningfull choices to make : spend ressources to have advantages ? use bless ? trying to attack with a %to hit that is not that good ?
Players would have to be more creative and they would have a better control of their %to hit with choices and tactical decisions to make (there are many ways in D&D both for melee and ranged characters including basic actions like help, shove to prone, hide, flanking,...)
My personnal opinion is that something like that would be better but I'm totally fine with those enjoying Highground as it is... But all this looks like facts and personnal preferences aside, I'm still waiting for someone to explain why something like this would be bad for the game.
Those that doesn't want to think about their %to hit already have loaded dices.
