Hime is very tomboyish for sure, but I hope that's not her defining reasoning if she comes out as a trans guy especially after being called a "boy" because she's outwardly aggressive
That would indeed be stupid because it's backwards: boys are usually masculine because they understand themselves to be boys, meaning they emulate the male role models and peers in their lives and have, to differing degrees, masculinised brains. The same goes for girls and it applies to both trans and cis people.
Criticising a trans character for aligning with their gender role though is just as weird as criticising them for not being "masculine"/"feminine" enough. And attacking this manga for being clichéd is... strange, considering there has probably not been a single one ever that depicted an mtf x ftm childhood friend high school romance, or an mtf x tomboyish cis girl if that's where it's headed instead.