What exactly was the point you were hoping to make here? Readers saw the chance for a trans character and for this to be labeled girls' love. Instead, we get yet another "Oh I just like cute things" and yet another cishet romance manga.
Senpai wa otokonoko.
Koisuru (Otome) no Tsukurikata.
Many more pieces in the crossdressing tag in which cisheteronormativity is favored because the authors are too scared to make a transgender character despite how the character was written.
Man, people like you are full of toxicity. It's actually people like this who give trans people a bad name and make it harder for society to accept them.
If the author intends for a character to be a straight man who likes crossdressing, then don't demand for him to be trans. That's like saying a tomboy girl to be a trans man because she happens to like non-girly things. If you want to read a girls' love story with a trans character, go look for a story like that. It's like going to a Chinese restaurant and complain that there is no hamburger on the menu. Why would the authors be afraid to make a character trans? Japan is not a hellhole where LGBT people are punished and killed like in certain places. I've seen them in other manga. They exist. It's simply that this author isn't making that kind of character.
Example: Naoto Shirogane from Persona 4. It's not that she wants to be a man. She wants the respect that men have. She wants equality.
While I am in favor of people living as the gender they prefer, forcing someone to be trans just because they like something traditionally manly or feminine is opening a new can of worms. There's a reason why women who compete in martial arts like MMA or serve in the military don't transition to becoming a man, you know?
I don't have any complain if Subaru does turn out to be a transwoman who still likes women. But if he isn't, that's fine with me as well. That's simply his sexuality and preference in clothing. Being able to pass as both gender is a talent not everyone has.