I agree some modifier is appropriate, but would prefer to see a +2/-2 (same as 1/2 cover), over full Advantage/Disadvantage. As it is now, it just seems to make one combat strategy far to powerful, and, IMHO, makes combats a bit boring; get high ground and ping away until dead. Move to next target.
They need to balance that a bit better indeed, right now it is a bit too much. Most of the time it is really hard to quickly get the high ground though, so balancing it will make combat easier, not harder. Most of the tough fight enemies get to the high ground really well. Think mama spider, rooftop goblins, githyanki with teleport spells. Having said that, do we have any projectile defense spells in 5e? That would change the balance dramatically in those situations.
