is this true, or is it something you think should be true?
Justin has fought 4x in 14 months in the UFC. at least 3 of them took the fight gladly.
Romero just signed a fight his opponent specifically asked for, and when he pulled out, the opponent is blasting him in media for not fighting. which is kinda the opposite of what you're suggesting.
i agree with the above poster: Cyborg. in men's mma, i have no idea. no contemporary fighter comes to mind (though AO in 2009 / Ubereem certainly comes to mind)