Explosive shells will provide a benefit to a much larger portion of our forces, since our primary fleet weapon is macrocannons. See the difference between our solid shots and explosive shells fired by traitor warships:
As happy as the Calavan gun mafia would be to go with that argument I suspect, Macrocannons and torpedoes have slightly different roles in the battlefield. More pertinently, the DPS of torpedoes is potentially vastly higher then that of Macrocannons. Except that, right now, they kind of aren't for us.
We lose in flexibility what we gain in power if we let the gap between line guns and torpedoes get too far.