Haha, you're not the only one who thinks that. I totally want to use him for something, but I've never watched the show, so it feels like a bit of a sham.
There's also the difference that the catastrophes that ended Aang's and Superman's peoples were not of their doing, while the Doctor is the cause of his. Could make the mutual sympathy a bit awkward.
The doctor would've fit in there just fine, too.
but i feel like the Doctor should be in here somewhere >_>