How I think about the TD's are like this!
SU SU85 for 120 fuel is very good and reliable. It always seems to penetrate most tanks and has good DPS for its role. No turrent which is its only main downside. It is also accurate on the move but no as much in comparison to Jackson I believe.
USF M36 Jackson costs around 140-150 I believe. It is the best I would say since USF can recover very fast with their vehicles. Has the range and the best part, it has the best moving accuracy making this deadly. Fast too.
UKF Firefly costs 155 fuel I believe. It has the slowest fire of them and the highest damage being 240 but its DPS in comparison is lower. I think why it is like as it currently is, might be because of their upgrade to rockets. That significantly stuns and damage enemy vehicles. Brits have access to as well strong, heavy vehicles. Might explain why its worse in comparison to the rest because of this fact!
I mean if you talk about Axis, their TDs, are not as significant a role as Allies. Since their range is all slightly shorter than Allies TDs. Less penetration also but enough to take on most but the heavy. That is why Panther is the only shot they really have. Even then, they all require Panther to suit in other situations that many allied infantry does better on AI areas. Panthers does help support for Axis overall weaker scaled infantry units mid-late game.
Su85 is 130F, its moving accuracy is the 0.5, same as literally every other tank in the game except the valentine, churchill, and all of USF.
Jackson 140F, jackson also OP imo.
155F is correct. FF damage is only 200 until vet 3 where it gets 240 per shot. The firefly is by no means bad, it just actually has drawbacks unlike the jackson. Its cost should honestly be swapped with the jackson in its current state.
JP4 has 60 range, matches allied TDs.
Fixed some stats for you