Weirdlet

You plan to only use the traditional D&D races?

So the Elves are Warhammer Highelves without the Dark & Wood elves?
Any special reason why upper-class and/or pure-blooded elves don't bend?

Suggestions: if the dwarfs lives/comes from underground then there is no reason why they don't can have cave openings, villages or even cities on/under some of the islands. The idea that dwarfs only live in the mountains is a cliché.

If the Goblonids are the standard D&D version then I suggest that they have weary few benders among them and the once who are often became Shamans or tribal leaders