I understand what you are trying to accomplish, but that would just solve the cause not the true problem. The real problem is that heavy vehicles and advanced mediums to lesser extent are just too cost-efficient. It's just more noticeable in large team games due to the higher resources. And no I'm not talking about the call-in issue, a small one time fuel advantage.
Heavy vehicles can operate and push without worrying about the vehicle suddenly dying to a well placed at defenses due to their high durability and sometimes range, and as long as they pull back before death and this will cost them nothing, especially since the dedicated AT can't give chase against even minor support. Medium tanks on the other hand are forced into attempting high risk maneuvers if they want to succeed against these vehicles which even in the best of cases will cause casualties for them.
They need to add some sort of cost to USE heavy vehicles so that cost effectiveness of the medium tanks actually evens out with the heavies
Currently that is done by popcap and upkeep, are you saying they should increase the popcap for heavies or do you think something else?