Let me put that straight... the firefly oneshotting tanks is a "skillshot" but the Sturmtiger oneshotting stuff is overpowered?
You said it yourself, its a cannon shot and two rockets.
It costs muni to upgrade and even more muni to shoot.
It can miss if you move, main cannon also doesn't have 100% accuracy or penetration.
Its on a fragile platform with mobility only slightly better then a heavy tank.
It have one job, kill tanks, its useless against infantry, single shreck squad can be its undoing because of its hp and mobility.
You are seriously comparing it to 5 fuel more expensive mini nuke launcher that with a single shot can obliterate tank and multiple infantry squads with no muni costs, with no warning(you'll get FF shot which will reveal its position before tulips fire), out of los, over shot blockers?
For real...?
Brits bring heavy AT ordnance into the field, deal with it.