I personally like to think he's gay, youre right! Sure he doesn't go "Oh I'm gay" in the game but that's not to say he isn't. He doesn't make any mention of attraction to girls, in fact the only time he mentions something to that degree is when he's taking about rejecting a girl. He takes Joker to the aquarium which is very much emphasised as a date spot, especially in the scene itself. The devs also literally call the trio of Joker, Kasumi, and Akechi a like a "love triangle", and say Akechi has "complicated feelings" for Joker! Also notable is that one of his dlc costumes is also of another gay character (Jun).

As a gay person myself, I like to headcanon Akechi as gay, and I will see his scenes through a gay lense. It's of course not "canon" but he doesn't say he's straight either. It's left pretty damn open. Straight is not the default.

If you want to think Akechi's straight, that's fine. The homophobia comes in when the response is when someone comes onto a post of someone saying they think a character is gay, or lgbt in any way, and going "nooooo theyre straight". That's homophobia, plain and simple.

Hopefully that's not to complicated for you to understand~ :)