They don't rely on out-ranging the panther.
SU76 has insane rate of fire, you can outproduce a panther with at least 4 SU76s
SU85 has self spotting and extremely good penetration
Jackson has speed and penetration and damage - and AP rounds and self repair
Firefly has penetration and damage, more than normal sight with 25 munition and retardedly overpowered tulips that stun your entire tank - sitting ducks.
in the past when panther's armor was potent, outranging might be true.
Now? any allied tank destroyer are buffed to neglect Tiger/Panther armor - combine that with longer range and self spotting shit like SU85, British command vehicle; panther can't get a shot in before half its health gone
But you don't get PV in order to deal with TDs unless you have somehow a bigger economy to sustain getting several of them and then relying on swarming a position, killing one and then pulling back quickly.
PV was designed to counter heavies and outslug mediums when ONLY SU was in the game (IS2/ISU and T34s). Too many things have been released and the OH PV just lag behind. USF is basically all mediums (unless Pershing or E8) with better infantry AI units (so while you could deal with mediums, Rifles can still over run you) and UKF has OP crushwell and Comet (Relic didn't know what to really do with Churchill). Live Piats laughs at PV armor.
PV is basically there for people who can't keep their Stugs alive
1-Having prioritise vehicles not affecting MGs will help PV a lot.
2-Su76 should see a really slight pen nerf IMO.
3-UKF vehicle commander should be nerf along with Crushwell/Comet.
4-Either improve RoF or keep it slow RoF but make it so it has a slight higher accuracy. Problem with PV is that by having attrocious scatter, there's few chances that a miss will still hit. On the other hand, AoE could be further lowered and improve scatter so it will hit infantry at a really slow pace.