This movie proves that formulas sometimes work better
Movies need a good guy and a bad guy, and then a final conflict between them. Period. It seems like an overly simple premise, until you see a movie like More Dead Than Alive. Then you realize how true it is.
Billy is the bad guy, for sure. Cain is the good guy.
So why not have the good guy kill the bad guy at the end? OR....if you want a twist ending, have the bad guy kill the good guy. That sometimes happens in movie, and it's cool.
BUT...what makes MDTA a bit ho-hum is that the bad guy gets killed by some other guy who's barely in the film. And then the good guy gets killed by some other character who wanders into the film about half way through. We have total strangers take out our two major characters, and this makes no sense at all.