why would you need a fuel price reduction? It can already kill the jackson in 3 shots while the jackson has to shoot 4-6 shots to kill it. And with that already signifcant advantage, the jp4 is going to shoot first because it has better vision, and after vet1 it is invisible. In general it is also firing at tanks that are much less heavily armored then axis tanks, and therefor has a much higher penetration rate. And better front armor and a lot more health. The increased fuel cost reflects the advantages this tank has filling the same role Jackson/SU-85 fills, but doing it better.
Are you sure the Jackson will need 6 shots to kill JP4? I've not seen jp4 bouncing Jackson shots. Does anyone know the stats on the toe-to-toe match-up?
Don't forget that Jackson has a turret, which is a significant advantage over a standard TD. Though the other points you made do make sense.