One Punch, One Kill

I've heard karate guys talk about their art as being so "effective" that "One Punch, One Kill" is an outcome. I wonder, how effective is a tool that can only be used in lethal situations?

generalist or specialist

In martial arts circles, you run into people who do only one thing, and do it incredibly well. You also run into people who try to do everything. Some of them are even pretty good. I know lots of guys who are great competitive judoka and MMA players. But they don't know anything about spacing or timing farther than they can reach. They know even less about hand held weapons. One question for people in combative disciplines has long been, "How do I train for all the different scenarios I may have to deal with?" I really haven't seen a modern answer to this question. I have my own solution, but it's not very modern.