There does seem to be some confusion on the point. Until a while ago things could fly much better, hence the dragons losing the ability so 'broken' flight is not a property of Avilona. There seem to be three explanations for it
1) Something changed in Avilona
2)Kasavarina and her team broke the connection when they were investigated the Ziggurat linked to avilona
3) The pillar from the ritual of the ancients had broken due to erosion making the connection weaker
IIRC if you use Avilona in the final ritual flying remains difficult so I think ultimatly something is wrong with Avilona, if my players get curious I will probably say Kasavarine broke Avilona.
I think for Gale I am going to go with her being a subject or accidental exposure victim of early pre lantern OB attempts to establish connections to other planes, which linked her to a different plane of Air, this will explain why the pc's cannot replicate her abilities