Difficult to say how powerful that roach actually is. I mean, yes, with the fire and such, but if it's a first level flamethrower, then it probably doesn't do that much damage in spite of being a continuous onslaught of fire. No, you need a DIFFERENT onslaught of fire to do REAL damage. It's all... I dunno? Hotter?
Room temperature fire is a thing, right?
EDIT: I'm being told this makes more sense than I previously assumed, because some things burn at lower temperatures. SCIENCE!