I'm of the opinion it performs the same as a jagdpanzer, just the JP comes stock with good DPS and gets defensive vet (17 target size+vet make it a pain to kill even chasing with meds). FF gets offensive vet and lacks DPS but a tiny bit more mobility.
Yet jp is cheaper and less popcap, imo this is the issue. Just a small price drop so they're at the same level.
It's also worth mentioning war speed and tracking are locked in a dead tech tier because the comet is a waste of fuel. I think if hammer wasn't so "meh" people would feel a bit better for spending 440mp 155f+muni on the firefly. As it stands noone us going to lock themselves out of the Churchill and OKW repair speeds just for the nerfed war speed and satchel charges.
i believe the m36 fits better as they have similar dps and pen
while the jp has lower pen and no turret so no don't compare price to it, it's like comparing the okw p4 to the Sherman and saying okw p4 needs to cost less