
No, the seme is an ass. You can be an ass and not be a bad person. Guys do things like that because they are afraid to face their own feelings. It is a form of cowardice found largely in men. They cover up their "weak" (normal) feelings with aggression. I'm a guy and I catch myself doing this all the time. Seme is immature so he got really lucky.

... you do get you are talking about a male fictional character created by a woman who needs to publish her story based on something she fantasizes/fetishizes about, meaning nothing to do with male psychology but more about what she finds attractive, that has nothing to do with male morals and behavioral analysis whatsoever but a lot more with what her page limit and her editos' opinions are, right? Good.
And I am sure you also get your connection to this character as a fellow dude is purely subjective, just as my theory is.
So I do not know how a male fictional character written by a woman who based him on her fantasizing material can be objectively seen (and so concluded by a real life man at that) as "an ass". I'm just throwing my opinion as a fellow fan out there, making speculations is cool by me, and you made an interesting point, but you can't just conclude that "this is what it is I know because I am a guy". It doesn't work like that, especially in yaoiland, which is ruled by women.
I'm always up for love-hate relationships but the end was a bit... underwhelming I guess.
I don't think the seme's an ass I think people who say that are just underage or something and think they are the perfect human beings that will go to heaven and if you have defects you go to Hell or smthing, I think it went more like:
OKAY WE NEED TO RESOLVE THIS AND WE HAVE AN X AMOUNT OF PAGES LEFT AND WE ALSO NEED A SEX SCENE, LET'S DO THIS FAST! lol