1- Different numbers (i guess you are counting flak + PA) cause the truck were free and same as before, fuel tech cost can't directly translate 1:1 and unlocking tech gave free bonuses (healing, resource conversion/mechanics, truck gun).
What i'm saying is you can't translate old performance OKW using their direct values.
2- Old JPIV was broken and limited only by the resources you could get. The unit is still beast once vetted, it's that it's suited towards defensive bonuses mostly. Something which is less desirable in high count player games where unit volumes might make it irrelevant.
Fuel cost for T4 was 80 which is 120 without the penalty.
Price of Panther had gone from 175 to 200 but not is back 185 and the price of PzIV had gone from 150 but now 140. In sort JP got a huge tech cost increase, a number of nerf and still has it high T1 price while PzIV is only 5 fuel more expensive that is original price and Panther 10 although their tech cost remained about the same.
The high price make PzIV a more attractive counter to allied mediums since its AT is enough and comes with AI also.
3: True. It might not be enough.
4: But i think it would strip the units from it's uniqueness if it has to be brought down to a 100/110f similar to the Stug. Penwise is already the same so in order to retain its 60 range it would probable have to had their vet 2 replace and lose the size/armor advantage. Rof would go down as well.
The size is similar to SU-85/stug , ROF is comparable with SU-85/Stug could be adjusted if there was a need for it.
Armore should be lowered and it will hardly make a difference. On the other hand, rotation, XP value and pop should be improved.
Then the unit would be better suited as medium counter.
Vet bonuses should be looked but that applies to most unit.