And also to be fair, heavy tanks have that 5m range advantage that, on maps with enough space to allow it, lets them get the first hits in on mediums AND dodge the first hits from mediums if they back up so that the med shells explode just before impact. Which just about assures the HT's victory unless they screw up aiming too much.
Mediums get higher-velocity shells that don't receive penalties versus heavy or mammoth armour - a trait that helps differentiate them from the light tank which is more for handling light vehicles, since it has a higher general DPS than the medium but does suffer penalties vs heavier armours.
Heavy tanks and medium tanks have the same health and armour so it doesn't really matter.
Doesn't seem to stop Soviets from claiming more wins than Allies (in games with high enough player counts that unit/map balance actually starts to matter compared to player skill) on Guard Duty or River Raid where the heavy is the Soviets' only choice of tank...