This suggestion isnt so much about the balance of heavy tanks as in "this tank is too powerful", but just in the meta game surrounding heavy tanks...
in coh1, if i remember correctly. Calling in a KT was a big deal. you only got one. Once you called it in, it usually triggered an important timing push for a VP, a major pivotal point in the game. In turn if the tank went down that was also a major pivotal point in the game.
I just recently got coh2. The main thing i've noticed is that there are a lot more heavy tanks, not just in the various different models of tanks, but in the number you can call in. In this replay the german called in i think 5 heavies by the end of the game, the soviet player who was down in points most of the game managed one in.. the game consisted of 6 heavy tanks in total. the german player didnt even tech to the point of buying regular tanks, his strategy after getting light cars was "just buy tigers":
https://www.youtube.com/watch?v=zHxNX3jLniw
Personally im a bigger fan of the classic version of heavy tanks where you buy one and it supports the rest of your tanks and the rest of your army. Its hard to take out but if you manage it thats a big deal. In coh2 I see heavy tanks get thrown around like theyre panzer tanks.
I think the game would be more interesting to see more medium tanks, and make heavy tanks be very expensive tanks to fill in the ranks, rather than being the entire army.
Perhaps it would be better that only 1 heavy tank can be called in the whole game? or maybe at least only have 1 on the field at a time?