While I agree with much of what you said, in actual fact the avicephalan
types were only considered thecodonts by the "anti-dinosaurian origin of
birds" folks.
Yes. One reason is that many others were (correctly) skeptical about the
presence of an antorbital fenestra in *Megalancosaurus* and *Longisquama*.
Another is that they saw that these animals have no other archosaur
features... diagnoses have always been malleable...