How is that "unfair"? Larian is creating a rule, that employs a 5E mechanic, Advantage, and applying it to ranged-combat from high ground. It's not about being "purist", as they are misapplying a 5e mechanic itself; it's unnecessary.
To be fair, Larian's addition of Height (and Backstab) Advantage does technically follow RAW.
The GM can also decide that circumstances influence a roll in one direction or the other and grant advantage or impose disadvantage as a result
BG3 is a video game where you can't ask the GM to grant advantage on a case-by-case basis, so it's perfectly reasonable for Larian to code certain things to always grant (dis)advantage.
However, while it's not unreasonable to claim that height should give some type of mechanical bonus (e.g., bird's eye view, removing effects of cover, disadvantage from low ground because looking into the sun, etc), height's prevalence in BG3 combined with the strength of capital-A Advantage is too overwhelmingly powerful. Typically, getting advantage from the GM in PnP requires some creative thinking and/or special circumstances. Larian's Height&Backstab require neither.
