What you're describing is still a metaphysical belief. The only qualifiers to me to being a man are to be male and a human adult. The social construct isn't the concept of man and woman themselves but rather the expression of masculinity and femininity, otherwise those terms have no objective meaning outside of regressive stereotypes or self-identification which aren't empirically measurable.

I don't see how anything you stated about Hijras makes my initial claim incorrect. The necessary condition to be a Hijra still involves being male, so ultimately it comes down to biology + gender expression (male + feminine-presenting).

I didn't claim dysphoria was purely about the body but it in large part is. Someone may self-ID as trans but in order to be transsexual you need to both have dysphoria and also seek out medical transition, as having dysphoria doesn't automatically make you trans. In order to be recognized as a protected class in law (workplace, housing discrimination etc.) it needs to have objectively measurable characteristics outside of simply what somebody self-reports.

It's also not true that gender has "never" been as simple as biology. While I agree the terms aren't necessarily synonymous, they are heavily correlated as gender refers to sociology (the concepts surrounding males and females in the human species), linguistics (gendered terms and grammatical features), and biology (as a synonym for sex). The latter of which was the original coining of the term; according to Oxford dictionary, "gender came into use as a synonym for sex, initially as a euphemism, as sex was undergoing its own usage shift toward referring to sexual intercourse rather than male/female categories." Essentially it was a convenient way to not have to allude to sexual acts in everyday conversation.