The problem isn't the Comet or the panther, it's the OKW.
the OKW panther cost the "same" as the wehr panther and perform almost exactly the same.
Wehr panther vs Comet is balanced because the Comet is a more expensive tank which had to sacrifice anti-tank power for anti-infantry power. A wehr panther will beat Comet most of the time, and that's okay since panther is an anti-tank specialist versus the generalist comet.
What to do with the OKW panther then? Taking the income penalty into account, the okw panther cost 50% more than the wehr panther. Does the OKW panther need to be 50% more powerful than the wehr panther?
The OKW panther preforms better than the Ostheer panther first of all because of the fact that the AI capability is way better, second fact is the 5 vet levels you can obtain. Yes it's hard to get, but lately with Brits I find it way easier to get my Panther to vet 3-5 which it completely obliterate any tank/infantry and with a JPz4 in the back it's GG mostly of the time.