Basicly. The M62 shell was a better round then the Standard US one. But the performance was less..
Theirfor, really, the ROQF 75 was simply the same gun as the sherman, but with less bullet drop. Theirfor more accurate.
Both the M3 75MM as the ROQF 75MM where designed as dual purpose guns, wich where designed for infantery support tanks. They where kept in service, because a sherman could still deal with the older german tanks, and kill the heavier german ones with some chance.
In the end, the allies where right in tank development. Combine firepower, armor(the pak40/75MM gun became standard and common only at 1943 mid) mobility, production numbers and reliability and you recieve the sherman and T-34. Both where well balanced on all of these levels. And german tanks where only better in terms of firepower and armor. And in the panther's case mobility. The stubborn german designers never standardized one tank. Wich led to their defeat.
Oh and hitler with "Hey lets make a Anti-tank version of the schwere gustav" idea's