I'm going to repeat myself, because I have the feeling that here again the word "advantage" is mixed with the rule mechanics "Advantage" in DnD 5e.
Height has its own advantage in and of itself --> so if a ranged fighter is on a hill, then he already has multiple advantages, meaning:
The fighter can't be reached so easily by melee fighters, he has higher range (--> parabolic trajectories) and if he takes a few steps back he has cover and can't be attacked by other ranged fighters. Those are several advantages, not just one, all by just being higher than your oponents.
No reason and definitely no need to also give the DnD 5e rule mechanic "Advantage" in addition here.
