I've been at skymark for almost two years. Yes, training (assimilate, cooperate, graduate) is difficult. The job (overnights) is kinda boring, and they're pretty cheap. The weather, I.e. winds and culture can be challenging. That goes with expat job. Those that are leaving have something "better" to go to. Many have been in Japan for many years and are ok with it. Some have no place to go for a variety of reason, and that includes screw ups.
I made US$20k last month. Sold my days off, resulting in 4. Flew 86.5 hours, should have been 94+ with "creative" flying. I will get a biz class ticket home for it too.
I am looking to come home, because there's no place like it....
I will say this is one of the better, if not he best, expat-commuting jobs out there if you can survive training. Japan is known for this. It's not a career position.