These treatments clearly don’t solve the underlying issue. The question is simply are they the best current alternative for a subset of the population. That is supported by hard data, even if the surgery is rather barbaric we simply don’t have the technology to do a better job while either keeping someone their old gender or swapping to another.

As to having a mental illness, that’s often how we describe issues we don’t understand or have the ability to treat. Stress ulcers are a great example of such classifications. I am not disagreeing that many of these people have significant mental issues, but calling something a mental illness isn’t specific enough to do anything with and tends to be used dismissively. Further once the underlying cause is discovered we stop thinking of say mercury poisoning as a mental health issue.