I think one question needs asking with the call-in heavies: what are they
for?
Every tank in the game fits somewhere into this triangle.
A purely AT tank (something that can't hurt infantry at all) is somewhere on the red line. A purely AT tank is on the blue line.
In a tank-on-tank battle between two tanks
of the same cost, the tank that's closest to the red line is going to win. A Tank Destroyer beats a generalist, a generalist beats an Anti-Infantry tank.
Therefore, the tank with weaker AT (the hunted tank) has to avoid the tank with stronger AT (the hunter tank).
Some tanks are very good at being the Hunted Tank. The Brummbar and M8 Scott can take devasting pot shots at infantry and run away behind AT walls when the Jacksons turn up.
The Panther is an interesting case. It's about 75% AT and 25% AI, so it's the Hunter Tank against generalists and the Hunted Tank against Tank Destroyers. As the Hunter Tank it can drive off T-34s and contribute a passable amount of anti-infantry damage on top of that.
As the Hunted Tank,
it's terrible. It's not going to win the tank battle, so it's contributing its anti-infantry damage instead rather than as well.
This is the problem Heavy Tanks have. Unless they're all in on anti-tank (Elefant, Jadgtiger) they're always going to be the Hunted Tank. Therefore, they've got be to good in that Hunted Tank role: smashing up infantry and weaker tanks, then running away when the TDs turn up.