One of the main issues with the harpoon is the massively broken mass. The pyra is the second smallest ship in the game, yet is one of the heaviest. Reason? To make it ram better... which has now been nerfed so ramming is a real gamble. Mass is one of the main factors in how the harpoon works.
The second issue is the velocity. An increase in speed and reduction of drop was being tested, but fell by the wayside somewhere.
The third issue is that even when connected, it does so little damage to anything, and rarely hits exactly where you need to get the effect you desire.
The last issue is the painfully slow reload.
I'll poke the devs about testing a harpoon with higher velocity, lower drop, more damage (especially to balloon), the ability to hook balloon as well as hull, severely reduced range and a slightly lower reload speed.