I've run this unit before a few times, and, to my surprise, torrent of fire is not an effective way to taken them down. They just shrug it off with the 2+/4+ FNP. Even if the odd wound gets through, you still have two per model, so it's by no means a big issue. The lone lascannon/melta shot doesn't really do much because you're always putting that wound on Draigo, who usually makes the save with his storm shield.
Units with a ton of melta shots have been the Paladin's biggest threat, so far. A unit of Fire Dragons (or melta CCSs or combi-melta spam Sternguard squads or similar) is great because each failed save is an instant kill, and there are so many shots you can't just allocate one at a time to Draigo, like the way you can with single lascannon shots.