It really ought to block all flying, then it's a tech choice, instead of an auto choice. It can't be dispelled right now, it's just a leadership test (which bretonnians have no trouble passing)
It's also not hard to get two big units of pegasus knights even at 2k.
The 2.5k list I played against had three units of 5/6 pegasus knights, and three flying characters on royal pegasus or hippogryphs.