http://ftr.wot-news.com/2013/08/18/m26-pershing-medium-or-heavy-plus-other-stuff/
Tank classification is not standard across nations. Within the context of WW II m26 Pershing was a heavy tank by all acounts. By the time they made it to the front there really werent any Heavy Tank things to do anymore.
Pershing is a straight equal to the IS-1/Tiger I during WW2, but then competes with
Centurion/T44/T-54 post war. Had the T-44 and centurion seen action(T-44 saw barely any) the same argument would be used against them.
Interesting read but it does seem to speak to my point.
The M26 was designed as a medium tank (american classification) and then redesignated as a heavy in order to boost morale. Then it was returned as a medium post war.
To quote your article "the M26 was built as a medium tank(that could still do heavy tank things), was used as a medium tank, and was called a medium tank before and after its stint as a heavy."
I would argue that the classification of a tank should come from the nation that produced it, within reason. Someone mentioned that the panther was classified as a heavy by the US (I have no idea if that is true or not) but it is now known to be a medium tank as it was designated by the germans.