You've got some good information here but I don't think you quite closed the loop to make a solid argument.

You're claiming, I think, that non-sex-dysmorphic gender-dysphoric trans population does not have any intrinsic "mental disorder". These people, according to your description, find it awful to have to take the gender role that society has set up for their body morphology.

How is this any different than ADHD, where people are generally fine with their abilities, except when society forces them to sit still and pay attention to boring stuff for long periods of time, and to do so in competition with others who can do it better than they can?

And yet we call ADHD a mental disorder. It is a disorder largely relative to the expectations of society. Most people can regulate their moods, thoughts, and behavior in such a way as to be reasonably comfortable participants in society in all the different ways we've construed it. But people with ADHD can't. (And guess what? ADHD correlates with depression too.)

So what you haven't done is make an argument that even in the case of gender dysphoria without sex dysmorphia, once it gets to the point where it's worth bothering with a label--and it starts provoking depression because parts of society are all "hey, we're not cool with that"--why doesn't it fall squarely into the pattern of what we consider to be mental disorders?

If you wanted to complete the argument, you'd need to argue that it's less like mental states that we do classify as health issues and more like those that we don't (although the designations change, so it's a moving target).

For instance, if you could argue that "gender dysphoria is a lot more like imposter syndrome than it is like ADHD or social anxiety disorder or anorexia" then you'd have completed the argument...at least unless imposter syndrome gets added to DSM-6.

Regardless of which bin we put various mental outlooks into, we also might ask: hey, rather than asking people to change to fit society, what are our options for changing society to fit more people?

That, I think, is really the core issue, isn't it? But it doesn't necessarily make it any more true for trans people than people with ADHD, even if the latter gets the "mental illness" label and the former sometimes doesn't (but does when it's associated with body dysmorphia??--I mean--we're not throwing those people under the bus either, right?).