I'm not 100% convinced than any sort of so-called "sex reassignment" is genuinely the best treatment even for severe gender dysphoria, but I'm willing to give it the benefit of the doubt for adults. But it wouldn't surprise me in the least if doctors in the future look back at sex reassignment with the same horror we look at Victorian-era doctors who removed the clitorises of young girls and women to stop them masturbating.

People don't always have a privileged understanding of their own mental state. We all know people who are desperately unhappy, and they think they know why they are unhappy but they are always wrong. I'll be happy if only I change my job. I'll be happy if only I get a boy/girl friend or get married. I'll be happy once I have kids. Or grandkids. I'll be happy if I move to another city. I'll be happy if I could only afford that car. I'll be happy if only ... if only ... if only ...

This is probably why, even before the massive escalation of "transgender" since the mid 2010s, the effectiveness of sex reassignment for ending the depression and suicidal ideation related to sex dysphoria was not great. Sometimes it helps, but often not.