I don't see why the Sherman shouldn't have been used in '44, it was more than capable of taking out it's main opponent, the PzKpfw IV.
The fact the the Germans had the Panther and Tiger makes many people think that the Sherman was rubbish, which does carry some truth if you have a 1 on 1 between a Tiger and Sherman. But that very rarely happened.

If the allies developed a tank like the Tiger, then the Russians would have probably got all the way to the north sea, OK that could be an exaggeration, but the war ended the way it did due to the speed, quantity, and the mechanical quality of the Sherman and Cromwell.
Just like the Blitzkreigs where won by the fast IIs.
Tanks like the Tiger suited the defender, while the Sherman the attacker.

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Patriotism is where the love of your country comes first, nationalism is where the hate of other countries comes first.-Charles De Gaulle.