But there were also numerous dinosaurs and similar creatures which were of similar weight as birds, and they died out. Heck some of them looked so much like birds that you would have to examine them closely to determine they were not. Yet they died too.
I think its more complicated. One thing I notice is that aves had an enlarged hip- they could lay much larger eggs per pound than the similar creatures. Pre-strike it did not seem to be much of an advantage. But I guess it allowed them to travel further while pregnant and have babies closer to self-sufficiency than the other forms.