Height advantage for ranged is ok. Flanking is also a thing so ok. On some maps it is difficult to get into an exact flanking position.
Any change can be used by the player.. and used against a player.
There will be an impact, particularly for some classes/ builds. If needed (and only if required) there may be ways to "rebalance" eg +2 to attack if reckless attacking whilst flanking. Perhaps with various changes we need to playtest all the classes to really see how they work in BG3, consider what changes would be best etc.