You were suggesting that using your hoembrew rule ,+1 or +2 for height advantage, would be better than Larian's usage of advantage
Because it is.
The problem with advantage in that context is not that is a bonus for gaining high ground, but precisely that it's a disproportionate one.
"Hey kid, the path to your school seems vaguely ill-frequented. Here's this bazooka. In fact, let's go to school in a tank".
even though Larian is using RAW(Rules as Written) (Pg. 173 of Player's Handbook "The DM can also decide that circumstances influence a roll in one direction or the other and grant advantage or impose disadvantage as a result."
That's a quote that is absolutely NOT proving your point. "Feel free to use it when it seems situationally appropriate" is not an equivalent of "Handle it around like free candy for maneuvers that are trivially easy to pull off".