If you hit someone on fire with the flare gun its a 90 damage crit and an extended burn time.
Yeah, it certainly isn't good at all.
If you hit someone with a shotgun at point blank it's around 100 damage and you can fire again almost immediately. In fact, the shotgun can actually out-dps the flamethrower. And as I said, fire damage is an incredibly stuffty damage source. That extended burn time won't mean stuff if the enemy has a targe, or is near water, a medic, a healthpack, a resupply cabinet, an allied concheror buff, or using one of the many self-healing weapons. And that's assuming the enemy lacks a brain and allows themselves to be hit by your flare. The flare gun is an interesting concept, but it's not good.