Are you establishing benchmarks? The natural progression of technology favors the modern tank category. Do you plan to normalise this by assigning compensation points? For example, if a single MBT is so hard to penetrate and has high mobility, it would have to deal with four WW2 light tanks.
Otherwise, everyone would simply buy or play as an MBT; there is otherwise no incentive in driving a tank that is slow and wouldn't penetrate your opponent.