DSM also thought being gay was a mental disorder. Caving to pressure is sometimes a good thing.

"Being born in the wrong body" is a phrase used to simplify a fairly complex situation in a way that also makes it seem like to trans people it's a metaphysical belief about the nature of the the soul. This is by and large incorrect. What trans people experience isn't delusion. Delusion relies on a belief that contradicts reality or relies on the very shaky ground of the insubstantiated supernatural. What trans people experience is an uncontrolled mental reaction to physical replicatable stimuli to their own bodies. All the cultural stuff is in service to this.

For example - When you call a trans man a woman - what that person is reacting to is your perception of their body making them ground in that physical discomfort. It is like if you had a physical feature you despised, say a physical deformation with a traumatic memory attached, and people kept remarking on it in conversation. While you might be able to walk the world happily temporarily forgetting it exists someone remarking on it is like shoving a mirror in your face. This is why misgendering doesn't have to be intentional to be hurtful.

Our culture has a lot of cultural protections built in for people who have deformaties through birth or accident because we understand universally the effect those things have on the psyche. It's impolite to stare, to mention or exclude people with those features. Gender however is harmless for about 98% of the population. It's remarked upon in the form of pronouns in every conversation where three or more people participate. This is ultimately why that saying "trans women are woman (etc.) " exists. It's not them saying that trans people have any misunderstandings or delusions about the history of their bodies or how they differ from cis women. They have no delusions, they are painfully aware, at all times, exactly how they differ. What that saying is trying to convey is that a trans person should not be treated or categorized by society any differently than cis people of that gender or should be accommodated for being treated as neither gender.

This is also why surgeries are often employed. It's in part to gain unwitting compliance from a population who reacts to physical sex characteristics and pairs that with gender. It's mending how people react to themselves in the mirror as much as it is removing the mirror from the hands of other people. What the removal of the disorder portion of the DSM was about was an acknowledgement that this problem is cultural. It is as much a problem with society's constructions and beliefs around sex and gender as it is a singular person's problem. Just as being gay is only a problem if society responds to it as an undesirable characteristic the issues with being trans are exacerbated by cultural sorting of gender into exclusive categories and people's personal ick about people's surgical and hormonal personal autonomy around their bodies.

The reason trans people have to frame their fight primarily as medically nessisary intervention is largely because of cis people's squeamishness causing them issues of lack of personal freedom to choose how to personally navigate a society not built to manage their specific personal struggles around their physical sex. The problem with society isn't going anywhere most places yet so the individual is assuming the burdens of that and it's well proven that those experiencing this issue are tackling that issue in thoughtful, logic based ways with proven ability to accurately judge risk and reward of their choices on that front.

Can you think of any other things that were previously classified as mental disorders but no longer are?

Maybe that's not a fair question, maybe I'm just being hysterical.