advantage for high ground AND disadvantage for low ground are just too much of a disparity (basically +/-10 between the dice rolls of two combatants on differing height levels). i could live with adv for (a reasonable i.e. >3m or 10ft) high ground WITHOUT also giving disadvantage when shooting or casting from low ground. or give a flat +2 bonus and -2 malus for high and low ground respectively. maybe this would be a good compromise, engaging with the verticality of the world is still encouraged and helpful but not as blatantly "THE thing to do". best case scenario would probably be a "custom game rules/difficulty settings" menu, so everybody could adjust the game to his/hers/their liking, the hurdle here being the AI, which would need to be aware of the rule settings and adapt to them.
This is why I would like Larian to focus on time implementing Cover in the game.
High Ground confers Cover when being attacked from Low Ground (+2 AC and +2 Dexterity Checks) and High Ground grants +1 To-Hit to those on Low Ground.
Then, Cover can be also granted to areas to add more dynamics (think of like XCom that give Cover for another good example) to the combat that affects tactical aspects of the game.
With this implemented, High Ground is granting all the benefits that players want as advantage, but not over shadowing all the Spells/Abilities that grant Advantage as per the DnD 5E ruleset.