I'm an academic, have a Ph. D., been published, designed and carried out research studies w/statistical analyses, am currently working on projects--sometimes with doctoral students on their dissertations--and I don't see much that is academic or scientific in the group you call "cultural isolationism." More scientism than anything else.
Jason Colavito was a graduate of Ithaca College--a respectable undergraduate school down the hill from Cornell University. But only Cornell has the graduate library with extensive holdings that Jason could have used to become an academic himself. I doubt that he ever made it up the hill.
The people you describe as "academic" are people I would refer to as professional debunkers using the debunkatron approach:
They call it science, but I wouldn't agree.
I'm more comfortable with the diffusionists and appreciate their efforts to understand--even when there is no data to support their speculation. After all, the first stage in science is always "guessing":
These days, we call it blue sky thinking.
For the most part, it appears that those you call diffusionists are at least partly blue sky thinkers, and the isolationists are professional debunkers.
Those of us who are truly academic--academic researchers using sound experimental designs and statistical hypothesis testing procedures--are somewhere beyond blue sky thinking, but much more tolerant of grounded research than the professional debunkers.