I frankly like my argument better,
viz., old birds replaced by new birds for reasons having nothing to do
with asteroid, but, rather, adaptations.
Undermining your argument is that "old birds" (enantiornithines) are far
more abundant in the Cretaceous than "new birds" (neornithines). Further,
birds were around for long time prior to the K/T extinction (probably over
90 million years). If they drove the dinosaurs (and pterosaurs) to
extinction, they certainly took their time about it.