Its like this. Think of a task that could be accomplished by a capship gun. The blobguns will fail at this task. They are essentially worthless. For every single role, FS2 has a different, better weapon. I'm really not sure why any ships have blobguns at all anymore (outside of balance issues).
If you speed up the projectiles, they become marginally useful, and can actually hit bombs. Bear in mind that a ship in motion (with bombs turning to track it, regardless of how slowly) will be basically unable to hit dick or squat, since the projectiles are so slow.