I still don't get what the point of the Dragonfire 'torpedo' is. It's a beam, meaning it's effectively useless against a target with shields, ...
This here is your misunderstanding. DEM weapons are
great vs shields, because it does 100% damage to them, unlike an HE weapon. A Gorgon does slightly more than double the anti-shield damage vs a harpoon; a Dragonfire does double the shield damage of a Reaper. Both are weaker vs armor: for Gorgons this makes them only moderately effective vs heavily armored targets, but Dragonfires still have 4000 penetration (half the penetration of a Reaper is still enough).
The weapons do soft flux, so the target can regenerate the damage without lowering their shield... IF the missile is impacting by itself vs a target with the room to stop firing and back off. The solution there is to fire multiple at a time, while also using other guns/missiles. If you fail to overwhelm a target with a DEM, they have a higher chance of recovering, but it is
twice as easy to get that overwhelm going.
Take a look at what happens when they are used as bombers, 1/wing:
Heck, give the thing Dragonfires and see how they do. 1 per fighter and watch the red death-beams fly.
pretty funny, ngl
Or, fire up a mission sim Onslaught and put all 4 as Dragonfires in a Linked group. The things
evaporates an opposing Onslaught, at the cost of using all its missile ammo at once.