Heavy tanks and especially in combination with veterancy is completely broken. If the player controlling the tank is somewhat decent and doesn't overextend, it is completely impossible to counter. 
To finish off a heavy tank backing away you need to chase it with Jacksons. In a majority of cases this ends up with your Jacksons failing to reliably penetrate, and getting killed either by the heavy tank or sniped by shrecks. The heavy tank gets away and is repaired to full. Pretty much GG from there. 
You can be even or ahead the entire game but if your opponent manages to save up for a heavy it is more or less over. You literally have to push your opponent off the map within the first 10 minutes to rule out these ridiculous heavy tank comebacks.
A large part of this brokenness originates from veterancy. If you manage to get vet 3-5 on for example a jagdpanzer it will turn into pseudo jagdpanther that can also easily take on at least two Jacksons. 
The ridiculous veterancy modifiers (and LMGs) is also what contributes to late game infantry battles turning into shit blobs.
Bottom line: Hit heavy tanks hard with the nerf stick, make them more in line with medium tanks. Tone down all veterancy bonuses, remove vet 4-5 from OKW (it is a broken idea)
QFT.
Its the veterancy that makes things broken.