Fuck yeah he is, but he'd get his ass kicked in an MMA ring getting thrown around by Overeem like that.
But as far as K-1 goes, hes definitely one of the best, especially as far as skill goes. Dude has some wicked combinations and power in both hands and knees. He's got very good kicks too obviously. He does leave himself pretty open sometimes though. He has a good chin to, he took a hard shot overhand shot from Sefo in their fight and just continued to beat his ass like nothing happened.
He definitely fights like someone just said something about his moma though, and it would be pretty scary staring across the ring at that psycho knowing your about to have to fight him.