"Patently false" is an opinion, same as any other, dude. Yes, it's true, some of us believe that, Momoa, while not necessarily incapable of acting competently, he does, more often than not tend to play himself in most, if not everything he does.
Jason's personality is very much aligned with the majority of the roles he picks to play. He certainly doesn't "disappear" into a role like a Heath Ledger, for instance. He is, at the very least, 95% Jason Momoa in all his roles.
Some cinema fans consider it a requirement of diverse actors to have more range in order to be described as "good." Something that Momoa sorely lacks... in my opinion ;b