Nah
I think Taiga was an idiot teenager hitting puberty, having his fated pair slammed into him right at the start, and was just parroting what society as a whole had been saying. He was young, dumb, and stupid with a level of hormones far beyond what we would have any understanding of.
The thing is though, that Taiga didn't stay that way. His regret was near instant. He instantly showed that despite his actions, he didn't want to out his friend to the rest of the school. He also realizes within days that he's lost his only chance at his fated pair. While his growth is slow, he does proceed to change over the next 10ish years. It gets accelerated when he takes in Rin.
He regrets attacking his friend. He regrets saying the things he did. He hates himself for what he did and the fallout that followed. He hates that he is just as bad as the guys who attacked his lover and makes him cry. And because of this, he changes.
I don't think Rin deserves to be alone because he wasn't really bad to begin with. He was just young, ignorant, and had not only extreme hormones but also the instincts dealing with his fated pair to contend with. All at the ripe old age of a middle schooler. But he reflected on his actions AND *changed*.
my second time rereading and I feel like Taiga deserves to be alone fr