I don't think the problem with the Panther is the Panther.
I think it's the IS-2 and Tiger.
Consider the following:
- The IS-2 beats the Panther in a 1v1 battle.
- The Tiger is a better heavy tank counter than the Panther.
Therefore, if you're playing Soviet and you pick an IS-2 doctrine, your opponent's overwhelming best answer in 1v1 is a Tiger doctrine. Going Tiger gives you 160 more HP, a load of anti-infantry firepower, and going Panther doesn't work.
What if we changed that?
What if we cut the IS-2 and Tiger to 960 HP, same as the Panther and Pershing? The Panther can then take on the IS-2 in a one-on-one battle, and the Tiger stops being a better pick than it.
Now that the IS-2 can be countered nondoctrinally, there's less incentive to go IS-2 every game.
Now that the Tiger isn't a better heavy counter than the Panther, there's less incentive to go Tiger every game.
This is a pretty accurate description of the problem, imo; but the solution only works in an OST/Sov vacuum. Reducing the IS2/Tiger HP is a good idea, but it means they'll be even more vulnerable to TDs, which makes '60 range TDs' an even more optimal choice.
As you pointed out, the reason the panther is 'bad', is because the Tiger is simply a better choice in every situation. I'd like to expand this idea to the other factions; the reason medium tanks/light TDs are bad is because 60 TDs are a better choice.
For USF and UKF, and to a lesser extent Sov and OKW, the best choice in essentially every situation is "60 range TD".
Enemy going for a medium tank? Get a 60 range TD and hard-counter it.
Enemy going for an AI focused tank? 60 range TD.
Enemy going for a heavy? 60 range TD.
Enemy going for a 'premium' medium? 60 range TD.
Enemy going for literally anything on wheels/tracks? 60 range TD.
Additionally, since those four factions have very strong infantry, they usually don't need the AI power offered by mediums, or already have some AI focused LVs built(Flak HT, etc.). As a result, there's really no reason not to go for a 60-range TD, as it shuts down any vehicle-based AI your opponent might go for.
To come back to your suggestion, as a result of all this, reducing the HP on heavy tanks in hopes of making the Panther a better choice will essentially do nothing, as other TDs will only be made even better choices in essentially every situation.