I can't speak for the others, but I think the choice between the Panther and the Jagdpanzer IV / StuG is mostly a player preference and/or map/situation dependant. One isn't necessarily better/worse than the other against similar targets. I'd say all of them perform roughly similar against most targets at the moment. The JP4 has the range and DPM advantage, the StuG has the cost effectiveness advantage (get two for 1 Panther) and the Panther has the generalist/brawler advantage.
The Panther however, is a mix of mostly mediocre characteristics. It has mediocre DPM, mediocre accuracy, kinda mediocre pen (for an AT vehicle), good but not fantastic mobility, held together with high durability. The complete package is good, but any one of those aspects on its own isn't anything to write home about. It is supposed to expose itself though, mostly by diving, where the current accuracy is often not adequate and it makes dives/attacks more risky than they should be. That is why it is being buffed slightly.
That being said, the accuracy buff is being toned down in V2. And if it turns out that the Panther with increased accuracy becomes too good, then we can nerf something else about it later.
I feel a lack of balance in your opinion, you've constently reduced SU-85 and Jackson stats so they don't become all-around TD counters even if their respective factions have no other stock units able to fill the gap but when it comes to the panther suddenly it has to become an all-around counter to medium, heavy and super heavy even if stug and jpz4 exists.
I really wonder why you don't apply the exact same logic for the panther: make it a heavy counter and Stug/jpz4 answers to mediums. Buff it ok, but to only be really effective vs Comets and above, and make sure it's not anymore the correct answer to T34,crom and shermans.
We're again all over circling back with this panther buff to the state where mediums have no place in game for the sake of one side having their iconic toy able to run over anything else.