I can't help but feel that, of all the starships, the Heavy Bomber is the least exciting. Every other starship has a role that fleetships just can't fulfill*, whereas Heavy Bombers just seem to do the same thing Bomber fleetships do, only less well.
They're tough and reasonably fast, and do high damage per shot (and high damage per second), at quite short range. They can't be deep-strike raiders, the Raid Starship already does that. Are they specialised anti-starship and anti-Guardian assassins, then? Could be a nice role for them, especially if they're also adept at taking on other big threats (hybrids, golems, spirecraft, even Hunter-Killers, Avengers, and AI Champions) that show up against particular opponents.
* Well, ok, there are quite a few fleetships that can reclaim, but you're not guaranteed to get any of them whereas the Leech Starship is something you can always have.