Japanese samurai would also have meditated as part of Shinto tradition, which had nothing to do with zen (except in so far as Japanese religion was quite syncretic, and blended things together a lot).

But they didn't meditate because it improved their fighting ability. They meditated because it was part of their religious tradition, just as medieval western knights prayed as part of their religious tradition. Not everything Asian existed for the purpose of improving fighting ability.

I'm dropping out of this one now though, because it's getting dangerously close to discussing something that is actually a modern religion.