I'm not so sure Tenzen is a ninja, in the end. It sounds to me more like he hates ninjas. If you pay close attention, at the end of 22 he says: "Iga and Koga, I'll make you fade away." Whilst hatred for Koga isn't uncommon among Iga (or vice versa), I think Tenzen has some different reason for his actions. It seems to me like he wanted them to annihilate each other, not one to win and one to lose. He doesn't show any remarkable fighting skills perhaps because he's not interested in such. And like Hakeem said, he can get the work done in other ways, so it's not vital to him.