I disagree. I tested this specifically by hanging out in an opponent's flame range to see if I could disable it before he set my stuff on fire. My gunner had disconnected, and we sat in it for a good two clips from the flamethrower. The highest I saw was a 9-level on the balloon, and that's after stationary firing for two clips, which means you need about 20s of sustained fire to get a flame-disable.
The point of a flamethrower isn't to get quick disables, though. The idea is that you're hovering somewhere above your enemy or are otherwise parked in their blindspot, which is pretty easy to do against Galleons, Pyramidions, and formerly the Junker, raining down a single gun that disables the entire ship at once while taking out the balloon and seriously threatening the hull, hopefully overwhelming the engineers should they have been unlucky enough to not bring chemspray. I don't know about you, but last patch it was pretty easy to get at least a full clip of flamethrower into an enemy as the gun has a very arc, it doesn't need a primary slot to function and it doesn't need a very long burst to force the enemy to either start wandering away from the hull or balloon or start sacrificing components.
Now, in my experience those level 8 fires will come up a LOT faster than what you're describing, my guess is someone on your ship had chemspray and you told your crew you were going into their fire. 20 seconds is more than enough time for components to start breaking under a flamethrower, I have no idea how your balloon managed to survive that long with an apparently slowly building level 9 fire when lower level fires will outstrip an engineer's ability to repair. Was that other ship ONLY firing a single flamethrower at you and not giving you anything else to worry about? If the ONLY thing you have to worry about is a single light gun (that isn't an Artemis) a ship full of engineers will generally be able to outrepair it.
You don't need a level 8 fire to disable a gun. A level 4 fire is more than enough to give pretty severe damage and turning penalties even on light guns, a level 1 fire will screw up Hwacha volleys almost to the point of uselessness. That's damage that happens immediately after a gunner repairs. Chemspray or heatsink will provide a hard counter certainly, but if all you have is a regular extinguisher you're still going to have to deal with your gun never being at 100% and dealing full damage. This is without aiming for your gun in particular, the engines and balloon and hull are taking fire too.
I made a LOT of use of the flamethrower last patch and the only reason I don't use it now is because the Artemis sacrifices the balloon killing ability (balloons are extra weak to fire) to be able to disable everything on a ship at long range without the need for another gun to force the ship to let some fires burn.
