Bradley's world class, but he's not KT's level by a long shot. Kostya stops him, makes him look ordinary. So will Pac if that fight gets made. In Bradley's defense though, it takes an exceptional fighter to handle him like that.
If Bradley could take flush shots from Holt and keep on coming, I see no reason to think he couldn't take Koysta's power. That being said, I actually think Bradley has the ability and temperment to make it an ugly grinding fight, where Koysta can not get a rhythm and he would win a close decision.