What everyone ignores for some reason is accuracy and target size.
No we have not.
Ok lets compare the JP 4 and SU-85 at vet 0
Accuracy:
0.065/0.05/0.04 vs 0.055/0.045/0.04
....
Target size: 17 vs 18..
The accuracy and target size is inline with the other case-mate TD the cheaper SU-85
For comparison reason
accuracy
FF 0.066/0.055 (at range 45!!)/0.044
M36 0.05/0.045/0.035
Target size
FF 23
M36 24
JP4 has a 96% chance to score a natural hit against a Jackson at range 60.
Jackson has a 59% chance to score a natural hit against a JP4 at range 60.
That alone makes a huge difference.
Funny that for example you choosed the allied TD with biggest target size and lowest far accuracy, instead of the SU-85 which is also a case-mate. I guess that choosing M36, that scores the lowest in your example, was completely accidental.
I also have to guess, that you accidentally forgot to mention that the same example on the move the JP4 would have a 48% chance and M36 44% (but also have to guess one can "glide shot" with slower non turreted JP4...)
JP4 can duel and win vs allied TD but chasing an M36 and scoring a kill is another story and actually the performance of JP4 vs other TDs is not the issue. JP4 is designed to win slug fights vs allied TDs.
The issue has more to do with the fact that one pays more than SU-85 for a unit that slightly better vs mediums and allot worse vs heavies.
If trying to claim that JP4 performs superior to M36 I doubt you will find many people to agree with you.
The JP4 will win a slug-fight vs a M36 but that does not make a "huge difference". Actual it make a small difference because very few people would use an m36 to slug-fight vs JP4.