Just take an Elemental Spell and learn it as another Element (Fireball->Acidball, Cone fo Cold -> Cone of Thunder, etc.). As long as it is not somewhing special like radiant or force, the GM should have no objections to that.
That should make all Dragonborn-Types more useable and balanced.
Not really. Makes acid fir example the best.
Fire does the best on paper but offset by all tge fire resistant sand immune critters.