Can someone explain why samurai would be tanks?

Samurai - brought a big sword for 1 hit kills, walked around in cool looking armor but was definatly not designed for any long drawn out fights, nor for deflecting many blows, but to kill before killed.

Ninja - known for being hard to catch and evading attacks which makes a lot more sense for a tank. Also one of these guys would actually have the stamina, manouverability, and dexterity to keep fighting for a long time, without relying on blocking like PLD or just manning it up like a WAR.