Sunbreakers' grenades are good in pvp too. There's the fusion grenade for the one hit kill stick, the thermite grenade for some zone control (a little bit at least), and the incendiary grenade which is from what I've seen good in pvp right now. "Lacklustre passive skills such as reduced charge time.....is charged"? Have you forgotten about cauterize, which is perhaps the most broken perk in the game right now and is half the reason why it is so hard to kill a Titan while they're using HoS (the other half being their absurd armor)? Cauterize is like hungering blade except it works for grenades as well. Flameseeker is also useful. At the very least, it grants an extra point of both recovery AND agility in addition to making hammers a little easier to land. Admittingly, their melee is bad because, like disintegrate and storm fist, it lacks the range and reliability. But the burn can cause the melee as a while to do quite a bit of damage.