Something Brannew presents as a rumor. Do you have a shred of evidence that they believe in it?
They know that for a goddamn fact since they had his dumbass locked up in Impel Down level 1.
Kuzan literally one-shot that clown on Sengoku's command.
That Mihawk is now working under a person who the Marines thinks is stronger according to you, you dumb ape.