I can't believe you still go to these numbers from tests in vacuum when you compare units. 230 armor vs 140 might have something to do with it. Time to kill doesn't mean anything whatsoever, given that you have to pretend nothing else wants to shoot at the TD while it just chips away at a heavy.
Jp4 can actually ping mediums/infantry AT trying to rush it which you know, might actually happen if your targeting a heavy tank with a Tank Destroyer.
And the SU85 costs 130 fuel not 120. Has since the reload/penetration adjustment.
Armour hardly matters since a) allied at has high pen anyways, b) it only really counts vs mediums and if the jp4 is getting hit by those, you've already made a mistake and will soon be out maneuvered.
And while I'm ranting, they nerfed it's vet 5 so that it's ambush (a one time) bonus only does 200 damage, which is incredibly insignificant. Compare that to the m36s hvap which does bonus damage and pen and the firefly's vet 3 which is perminant.