Not sure why you think this is an inevitable outcome of such disorders.I don't, not at all. Things arent as bad as they used to be, but there is still a stigma to being mentally ill and an attitude that the religion should be enough to fix your problems. I have been out for a while, but from what I read here, things havent changed that much, its not acceptable to admit you are unhappy.
Given the distrust of "worldly" authority, the belief that they live in a "spiritual paradise" and their fear of "bringing reproach upon Jehovah", its not hard to make a case that Jehovahs Witnesses are less likely to get adequate mental health care than average. So using only statistics on how many Jehovahs Witness seek mental health care is not really a good indicator of whether they actually have more or less mental illness than average.