You've nailed it. The whole "wrong body/brain" argument is pretty absurd: it relies on a tiny sample of people who reported gender dysphoria, a mental illness. In the same way that happiness and depression, which are mutable states, can alter brain structure when seen under fMRI, I guarantee that gender dysphoria can make a male brain appear to have female characteristics - even though theres supposed to be no difference in the first place lmao - and that resolving the dysphoria would reflect on a future scan. Im not saying that there arent legitimate people who are transgender, but its a fraction of a percent and almost entirely the intersex or people with genetic issues. The rest are as you said, with some people likely coping with childhood trauma and some who are sensitive to pseudoestrogens in the mix.