The problem with this refutation is that it’s incoherent. What is the author refuting? That some people think that there was no Bering Strait? That some people believe no migration ever occurred by that route? That there was no ice-free corridor? (One of the commenters points out the same thing.)

When it’s not even possible to ascertain what your refutation is refuting, you have failed.

I believe the author is attempting to state that earlier waves of migration via other routes do not disprove that later migration occurred via the Bering Strait route.

But like many poor writers, the author cannot state the thesis outright as then it’s too easy to challenge and face-saving is impossible, so it’s buried and incomprehensible.