Honestly, that’s garbage. A significant amount of people want Samurai/Bushi, Ninja/Shinobi, Wu Jen and such as proper classes and I cannot see a reason why we couldn’t work with an oriental concept such as Ki or the Kami.
I just don't see where "the power of yourself" which is Ki is different from Martial, which likewise arises out of skill, training, and discipline. There's a FLAVOR difference in the sense that Chinese/Japanese legends attribute a bit different effects to evoking this power.
The problem with Ki specifically as a power source though is, its just a place to dump a bunch of classes because they're Asian versions of archetypes. I don't think that's a good reason to do so. I think we can argue about if Samurai should be a class or a theme, but that's a different argument. It should be a martial character. Sure, he may yell "KIYA!" when making a nasty sword chop, and maybe that's a manifestation of his use of some sort of class feature (or whatever the mechanic is), and that's fine. I mean its not like the existing martial classes don't do similar things perhaps. I mean, really, you could just pick up the properly styled arms and armor, fight in the right style, and act appropriately, you're a Samurai, class hardly matters there (though presumably fighter is probably what you'd pick for that in most cases).
Truly, if Ki WAS going to be a power source, then it shouldn't be called that, it should have some other name that indicates internal power. That way it could have a normal array of classes of whatever sort and wouldn't be a magnet for every class that happens to be themed Japanese.
I don't even think that a lot of what is depicted in Asian legends/stories/movies/etc all necessarily appropriate to be called 'Ki' or any one other thing anyway. Clearly some characters are channeling spirits, others are simply expert warriors, and others have arcane knowledge, pacts, etc etc etc. Its just as wide a range as you'd get from European legends and such. It would be a shame if it all got folded into a single power source.