I'd say firebolt with perks is op comparatively to other bolt grenades. A bolt grenade is effectively a wide area impact grenade. Naturally the balance point must be a weak damage output. This was Bungie's conclusion on the weakness of the grenade type. The counter point is that it requires the use of 2 perks to do so, but those 2 perks each boost the super and or melee as well. The other method to dealing with this aside from a damage reduction would be to put in a non class based counter to bolt grenades (ex stand still, crouch, or shot the axion bolts). The end result would be reduced effectiveness for non line of sight targets, while either maintaining a damage advantage and or a distraction advantage in a direct fight. Stopping moving, crouching or trying to shoot a bolt will likely give the bolt user an advantage in a gun fight.