I would prefer they cancel also the height advantage, but if they can't let go at all, why not a +2 bonus; that would a home brew rule not too OP
Yea that would mean :
1) that the advantage mechanic of D&D is safe. The game opens to many strategies to improve our %to hit. 2) we have another possibility to increase the %to hit through highground/backstab that would work arround our positions. 3) we have bless.
I guess that with : advantage possibility + highground/backstab bonus possibility + bless possibility + modifiers + proficiencies + weapons bonuses... No one would still complain about "missing too much".
"missing too much" os not really a problem to me but it looks like it's something that bother many players so they'll have to care about it.
If Larian's dices are not cheated, this looks like a pretty balanced solution that would make this "constraint" reasonably easier to deal with.