Ki mystic isn't a trap archetype. It has uses for some monk builds, all of which require a smart player who can manage a relatively limited resource. The only thing that hurts at all is losing diamond body.
Its ki mystic ability > still mind. Bonus 2 ki and an additional use for the points (+4 insight on any skill/ability check as swift is nothing to sneeze at).
Mystic insight > purity of body. Letting your allies reroll attacks/saving throws is terrific support, well worth losing immunity to diseases.
Mystic visions and mystic presence are meh, but I personally am fine with having SR go far, far away from my character with good saves. Losing immunity to poisons hurts more than the disease immunity going away, but Fort save should be high on any monk. YMMV with being able to dream up divinations, depending on your GM.
Mystic persistence is awesome but ki inefficient. 2 ki/rd, swift to activate, you and all allies in 30' roll two dice for all attacks and saves? Yes please. I rarely play at 19th level, so losing empty body doesn't seem like a big deal.