So, if we wanted to make the Harpoon a "real" gun, I have on simple fix.
Make it pull entirely toward the user's position, without moving the user's ship. Currently, it's based on the mass of the harpoon and 'poon-ee's ship. This change would be unrealistic, but it would make it actually useful. You could use to drag enemies out of formation so you and an ally could isolate and attack. Or, pull an enemy into a minefield. It would be gun worth taking-instant, if temporary, chaos against enemy teams, and a chance to get good at a weapon that rewards user skill.
If they changed the harpoon so it pulled your enemy into you, I'd be willing to put it on the vast majority of my ambush ships for the surprise/isolation factor.
Thoughts?