No fly system pls. At the moment the foes can jump / teleport. So they always go for your mages. If they can fly the fighter are complete useless for protecting your mage and you have to run after the foes all the time.
You're right but flying is a way for a mage to avoid melee.
And too many enemies have been given teleport-like abilities. Larian gameplay designers are actively working on making Threatened not mean anything in BG3. Perhaps they don't understand the concept of Fighters locking down enemies in tactical combat.