Overall I think the flamer is balanced horribly right now. It's devastating when fielded against inexperienced crews to a point where some consider to quit playing the game over it. At the same time it's way too unreliable when used against experienced crews - to a degree barely anyone dares to use it as a primary weapon.
This is a problem that Muse is also trying to solve because the flamer is really difficult to handle for newer crews.
Aside from disabling ships that
don't have active chem cycles, a viable flamer use against experienced crews is as a
disable follow-up. This is notably on a Hwachafish, the flamer to buys time for a Hwacha reload and ship repositioning for a better second volley.
I've decided to study the sequence and numbers:
Hwacha reload: 14s
*Flamer suppression*
Light gun rebuild: spanner 6s, wrench 7.3s (assuming 1 person rebuilding)
Forced chem spray: 5s
(Return fire: 3s or 1.7s)
The force on chem spray means the light guns don't get fully repaired for a full 5s; they work at less than 40% efficiency with very poor turn speed. In a common Hwachafish vs Pyra scenario - without the flamer follow-up, the Pyra's light guns will easily get fully repaired and overpower the Hwachafish. Executed well, a Hwachafish can completely disable most ships in 2 volleys, and quickly leave the engagement to help with other ships.