AIT Theory Visited

An interesting post I found on AIT :

Large amount of literary evidence(Vedas and huge body of work in sanskrit) of the "Aryan Civilisation" exists but no literary evidence of the "Harappan Civilisation" exists.

Conversely, large amount of archaelogical evidence(Harappa, Mohenjodaro) of the "Harappan Civilisation" exists, but no archaelogical evidence of the "Aryan Civilisation" in the same scale exists.

If these are different civilisations shouldn't both literary and archaelogical evidence exist for both of them?

Putting these together, is'nt it plausible that both "Harappan" and "Aryan" civilisations are one and the same ??

I also have another crib about the AIT debate? Wherever the debate rages, it is made contingent on the anti-AIT guys to prove that the invasion did NOT occur. Rather, from 1st principles, should'nt the opposite be expected, ie, prove conclusively that invasion did occur. Taking the invasion as the "Null Hypothesis" and expecting people to disapprove it is quite inappropriate I believe.
Then anyone can claim anything, say, "Today's germans are not from germany, but migrated from the moon". Now prove it otherwise.