Two tons lighter than a Sherman, does it qualify as a medium or heavy main battle tank.
The M26 Pershing a 41 tons was designed as a heavy tank (latter downgraded to a medium tank).
I’m no expert, but I think that the proper way to think about it is that Tank Classifications were defined more by tactical role than physical design. Since form-follows-function, you get general charactaristics (Gun Calibre, Armor, Engine Power, Radius of Action) that tends to hold for each class, but with notable exceptions.
The Medium Tank Class kind of morphed into the Main Battle Tank as I understand it. The US never really built a true heavy tank until the M1 Abrams. But by this time the Heavy tank class had fallen into dis-use, so the M1 family is referred to as a ‘Main Battle Tank’.
Recently I did a lot of study on WWII tanks, (hobby) and actually the British used a different systm altogether designating tanks as infantry or cavalry style.
Infantry tanks were expected to keep up with the infantry and were not designed for hardcore mobile warfare. They were also heavier and better armored.
Cavalry tanks were designed for scouting and mobile warfare at speeds that infantry or slower tanks could not match.