I think it might be neat to adjust fire stack chance based on current fire stacks, so prolonged flaming becomes a diminishing return. This would be more tolerant of extinguishers, and we could make each individual fire stack more significant in some way, see below.
The 'fire stack disable' could be implemented as fire stacks subtracting from the component's maximum health, so its new peak performance is worse than before.
I've been bouncing an idea around for a while that fire stacks on guns/enginges should increase by themselves if the component spins/fires, so if your gun gains 1 stack and you keep shooting the fire stacks grow on their own. Same for engine, if you don't stop burning the fire stacks increase.
Honestly it's a really difficult problem, how to make flamer balanced and fun at all levels. In tf2 for example fire works much simpler, there is no chemspray equivalent (vaccinator kinda works but sucks for other reasons) only extinguishers.