the question of what should be tha panther's role is not tough. Panther should be the linchpin holding the wehr together in the late game.
The wehr's biggest weakness is their lack of durability and mobility. Panther having high armor, high hp, and good mobility (6.4 2.3 is still good) essentially plug up the wehr's institutional weakness.
The panther give the wehr something that can carry an offense and take damage. In fact this is really what most people used the panther now. It's already used as a heavy by the axis.
The high moving accuracy is a USF trait. Historically their tanks was the only one equipped with a stabilizer, although lend lease tank also kept it.
Wehr, okw, soviet, and the UKF all have to deal with a .50 accuracy modifier. the Firefly conversion process removed the stabilizer, although it still have a .55 accuracy modifier that's marginally better.
Stugs are a working solution for offence as well. Why bother with a Panther when two stugs do just as fine if not better in the same role?
Durability is not really an issue most of the time when you can burst down armor in a few quick volleys so the chase is not even needed often. Also trading stugs is almost always a good trade while keeping especially allied TD numbers in check.
If one is really struggling with their durability, a command P4 and smoke will compensate. If AT guns are being a problem, a brummbar or a werfer will help with that. Brummbar vet 1 can delete AT guns head on and can take several hits. (So why pray that the Panthers armor and HP can handle the AT guns and whatnot when one can just get rid of them entirely?)
The original issue still won't go away. Panther Can be used for offence and it Can yield results. The Stug can be used as well but it Will give you reliable results, while it doesn't necessarily require the stop to fire babysitting thanks to its RoF .
What is the incentive to get a Panther when the T3 TD will still outperform it in most cases and is much more cost effective and flexible in its roles? (and I'd even say the Stug is the linchpin holding wehr together in the lategame, not the Panther)