"Ki" as a culturally laden way of describing certain useful ways of breathing and applying good body dynamics based on the subjective way they feel rather than medically precise terminology = totally fine in my book.
"Ki" as a magical force granting supernatural powers which can only be achieved by studying arts which use that culturally laden terminology = fantasy.
"Mastery" is a highly subjective word which is used to describe a wide variety of skill levels. It's not necessarily a bad word to use, but the martial fantasists often apply it based on a very unrealistic perception of their instructor's or their own skill level.
"Enlightenment" is a term so vague and subjective as to be almost useless in general. It can be narrowed down to a somewhat more precise meaning in certain religious contexts and there have been some psychological studies of the kind of subjective mental experience which is commonly described as "enlightenment" in those contexts. However there is no particular evidence I've seen that martial arts training is especially likely to lead to that experience. Furthermore, martial fantasists who make a big deal out of achieving "enlightenment" typically seem to have a more pretentious idea of the concept, thinking this "enlightened" status makes someone especially wise or possessed of esoteric knowledge or qualified to be life guides for others.
That's been my experience, anyway. Your mileage may vary.
