there is a mismatch between their gender identity and their sex
A mismatch requires you to believe there is such thing as a match.
To acknowledge a match, eg woman matches female, you have to acknowledge there is something female about a woman, to know what a a TW is identifying into.
You are claiming either that there is a set of personality traits that "match" your body.... or, as I said was the more sympathetic argument, that so many people believe there is, that this match may as well exist. If everyone is going to stereotype you, why not at least switch the stereotype to one that you feel is closer to what you're like?
(I guess people do this in subtle ways anyway , "expressing themselves" through clothes- trying to look like a sporty person, urban, fashionable, geeky etc. As there's not really any harm in, say, thinking someone is sporty when they're not we don't say "tracksuit wearers are runners, deal with it". Or "glasses wearers are intellectuals, deal with it".)
But when it comes to being dishonest about your sex, that's where we draw the line. Sex matters.