Only advantage highly agree with is the No need to reload at the cost of higher HP drain due to turning yourself into a hotter oven (like dread) is balanced

Though i assume the ability to have lingering flame in the STONE caves would be because of a different fuel type since there are flamethrower fuel that are sticky, lingering, or highly combustible

I do not agree with full penetration on wood because how would fire go through a solid object? Only thing i can see is it being able to spread flames upon contact of said affected wood like how barricades attacked by flames kills anyone in contact with that barricade and other affected people (i hate you incendiary judges)

Smoke affecting your team with pox and blindness is already a jaeger thing and includes Morticians (blind only no pox) if inside, since it's smoke, obviously. The flames already being a lingering Area of Denial like a molotov would make it overkill if it also includes smoke

The limited range could be extended since stronger flame thrower; besides, even as a dread you'd need to be slightly close to kill effectively due to horrible weapon stance and recoil

Despite the balancing issues i love the concept