I got this idea from a recent discussion on feat balance & character customization/uniqueness.
What if all characters got a flat +1 (or +2 or +0) bonus to attacks from High Ground, but there was also a feat that gave you +1 Dex and Advantage on attacks from High Ground? (This feat would probably replace sharpshooter since there is no Cover in BG3)
Similarly, what if there was a feat that granted you advantage on melee backstabs? (No bonus without the feat)
I feel like these would be fairly balanced, allow characters to be more distinct in playstyles, and be a compromise option between the "Yay High Ground Advantage" and "Boo, RAW don't give a bonus for high ground" camps...
I think a feat that gives the player easy advantage on attack rolls would become an auto-pick. War Caster with advantage on con saving throws is a really strong pick. Maybe a +2 to hit from high ground to replace sharp shooter and a +2 to hit from backstab as feats.