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 advantages. +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 or break the ennemie's lign of sight).
What would change is that highround and/or backstab wouldn't probably be enough to have a satisfying %to hit. Players would have to be creative to increase it (there are many ways in D&D both for melee and ranged characters including basic actions like help, shove to prone, hide, flanking,...)
Well that's what apparently passes as a fix in BG 3 not to use it. Why i don't know but that's the take from Larian so far.
THere is no reason to be creative when best option is always just to nuke stuff due to low HP. Why cast bless or whatever when you can just use something that will give you more damage you only have 4 Concentrations to use and low action economy. Even stuff with more hp dies fast..
And without good highground bonus i will not even bother with that. Right now it's the only rewarding thing in the game. When i get to highground i get the feeling a actually did something tactical. Maybe that just me. But i do agree that backstab feels like chees due to jump/disengage. Melee are now just frogs..:)
That's really strange to talk with you because I agree with many things but we really think differently^^
What you said also apply to highround and how Larian give us advantages

There is no reason to be creative when best option is always just to go higher to increase your % to hit.
Why cast bless for a +2 to +4 bonus to attack roll when you can just backstab or go higher to have a way better bonus to your %to hit ?
A +2 bonus
is a good bonus, especially if it stack with usual advantages or bless. As I said a few tweaks on the maps could also lead to more possibilities to "cover" in many situations. In BG3 all weapons have the same range. Isn't it a good bonus to have a better range than your ennemies ? isn't that one of the MAIN goal of being higher in history ?
I also have the feeling that going higher is something tactical in the game... But I'd love to have MORE than only 1 or 2 tactical possibilities and reading to you I'm sure we would agree.
Keep also in mind that a lot of D&D stuff to have an advantage are build on synergies between your characters... And I'm sure you'll agree that BG3 lacks of synergies.