Right now, KraiDuo is about the most powerful thing at their disposal.
What vivvav said.
Of course, Duo may not be used to his new body yet...
heh, Kraid doesn't look very imposing, aside from his size. He's all fat and his legs are so short he can't move very fast. Maybe he can get creative with those stomach missiles, or perhaps he has some hidden Duo power in there?
You know, Samus always had a ledge to stand on or something and could shoot Kraid in the face. Sometimes you had to jump up his belly button missile spike fingers to shoot him, but this doesn't look like a closed off room where that could happen easily.