Agree with the OP in large part.

I like the idea of things like high ground and backstabbing providing some bonus, but I don't like how it just uses advantage, one of the biggest bonuses you can get in 5e. +1 would be more than enough to make it worthwhile to play around tactically; but not so effectual that it swings the entire battle and more or less is the deciding factor in who wins and who loses. These games should be about who makes the overall better decisions and spends their resources better, not just who can constantly keep high ground/backstabbing advantage.

If these changes don't make it in-game, you can bet I'll be looking for mods to change it.