Lastman is right. It is pretty clear that high ground giving a significant benefit is part of Larians vision of how the game is supposed to work.
I, personally, would not bother much with high ground for anything less than +2 / -2 and I think the same is true for many other players.
Developers usually want to incentivize playing the game as "it is meant to be played", so even if they should change the mechanic, a significant high ground benefit will most certainly stay.
On a side note: Yeah, turn ending attacks and overwatch for an actual tactical game would be awesome
