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I agree with the general notion that high resource games currently favour heavy units, albeir for different reasons.
High resource games are usually 3v3+. Combine this with laney and small maps that are 1) easier to defend and 2) there will always be a lot of concentrated firepower, lighter units will just be deleted more easily than in smaller modes. Major advantages of mediums like high mobility also don't matter as much the larger the mode becomes.
Comparing two mediums to one heavy does not really make sense.
Yes, losing one medium compared to half health of a heavy tank is obviously more expensive. It is meant to be like that. Two mediums still offer the huge advantage that you usually have at least one operable, that you have higher mobility and flanking opportunities and (potentially, not sure about this one) higher AI firepower.
Discussing this without context will end up in a debate that just keeps circling, because one guy is debating over 1v1 and the other over 4v4.
These modes are hugely different, and so often is the role and cost efficiency of vehicles.
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There are quite some factual mistakes in your post, but as Esxile already wrote:
Reality has only been a very rough guideline for any strategy game that wants balance. Usually they are only followed as much as necessary to not completely destroy the expectations. CoH2 is no simulation game, most of the community does not care if the in game models stray away from the actual performance.
That would also be hard to do. There are so many variables, starting from differences in steel and build quality between factories and years to other simple things like differences in armor of different parts of the tank, angling etc. All of this has to be simplified into a handful of numbers, otherwise we'd end up with a sim, not CoH. Most of the elements like critical hits etc that actually convey more realism have been removed from the game to make it more balanced and less frustrating.