They improve greatly, and sometimes I go and see the performances they do and I am consciously aware that there isn't enough work for the good dancers.
I maintain that if you're a novelist and you go into an art museum, you'll come out a better novelist. And if you paint a picture for an hour you're a better actor at the end of it.
In the world of classical ballet there are only a handful of story ballets, so getting a new one is cause for excitement.

