The problem with trying to make this assumption is that it simply doesnt always hold.
For example, The soviet T-38 was arguably superior to most German armor as early as the winter of 1941. While I wouldnt necessarily disagree that the german's made some stellar improvements in tank technology - they were by no means in a class of their own. In fact, I wouldnt be opposed necesarily to there being individual stats for tanks, but if the German Panther exists with superior stats to the Sherman, then the Sherman ought to be compensated for either a faster creation time or less ICs per unit.
More to the point - German advantage in tanks shouldnt come from having inherently better units, but for being better at using them. This manifests itself in land doctrines.