Yeah, it's a bomber. the easiest evidence in this regard is the fact that they were the Alliance's first choice to take out the Death Star, which is why they went first. They have a high capacity for torpedoes and heavy armor, and they approach at slow speed in order to better hit their usually-stationary targets. Their torpedo racks were exchangeable with missile and bomb racks, so they could be adjusted for their roles.
As far as the game goes however, they fulfill the bomber role just fine. Torpedoes work best on what, exactly? Right: targets with low agility, or no agility. They also have the heavy armor necessary to survive long enough to deliver their payload, and slow enough that they can deliver their torpedoes without overshooting their target.
Seems like a good fit for the bomber role in this game.