This team was never optimal for this fight. He was doing it for fun just to imagine a scenario where gilgamesh came face o face with Ivan and seeing that he had discarded most of his human body to become a disgusting half beast, gilgamesh would want to cut him down. Also, this version of Ivan was not even weak to enuma elish because for some reason he dosen't count as a servant. If he wanted to, he could have used a powerful ST assassin like emiya and killed him easily. He even mentioned that at the start.
