But I think the basic idea, by itself is harder to dismiss
Archeology by itself is always going to have limitations, and there are vast swatches of history we are almost completely ignorant about
EvD is certainly guilty of taking himself much more seriously than the evidence suggests. But there's always going to be that "what if"
Its an unproven hypothesis.
It doesnt need to be "dismissed" it needs to be proven. You could make up any number of hypotheses. You wouldnt "dismiss" any of them. If you were interested in one you might design a test to prove it. But failing that its not worth worrying about.
When you write like 49 books trying to convince people of your untested claim, it seems like grifting instead of working towards evidence.
That said, it's still an extremely low probabilty that life from other systems came and visited our particular rock some time in the past million years (and interacted with humans).
You don't have to agree with it. But the lack of evidence doesn't disprove the hypothesis. Yes it doesn't prove it either.