Definitely a plausible ending...
It definitely makes sense that a Caucasian with three weeks of sword training by a blacksmith would be more than an even match for a Japanese martial arts teacher who studied most of his life. It's not the size of the sword that matters. It's the ruthlessness of the man who wields it. If only Oppenheimer had learned to use a sword instead of creating the atomic bomb, he could have shown the martial arts world the true meaning of the Four Horsemen of the Apocalypse.
What made Kinjo so good was that he didn't care who he killed or how he did it. If a guy turns his back, go stick a sword in it. If a kid or a woman carries a sword, they're fair game to disembowel.
Now, Takeda wouldn't even let Racine shoot that ninja on the train with a gun. That's such a lame code and for that he deserved to die.