He's never been in a situation where he's had to be mindfucked.
Even though Hosakafags BAWWWW about how it's the character that counts and not the series he's from, the series actually counts for a lot. It makes you think about how one character would react put into the other's situation.
In this case, we're putting Hosaka, who we've only seen in a quaint, high school setting, into a dog-eat-dog world equivalent to hell. When has he ever faced losing a limb, his freedom as a human being, or his very life? Because of the nature of his series, we're not going to, so we can't be sure as to how he would react to such a situation.
Not saying that Hosaka might not be GAR, because hell, he could be. But we wouldn't REALLY know.