i did it... i won a flamethrower game without splinter or rubber bullets i feel so powerful
first get your hands on as much hp as you can diamond and shana do fine then unlock the entire multi shot and pyromancer upgrade trees after this you can go for hp and speed upgrades for overall defence but also to unlock rage and run and gun dont take the gigantism upgrade until late game when this build is fully online
finally take the tome of power not the tome of rage percing is better for spreading fire than fire rate and you need the knock back
if you do everything right you should be able to face tank the entire game good luck