The Sherman is at least playable. The Crommy is 10 MP less, and has just worse AI, AT, and survivability. After the fat nerfs, its just brutally out-classed for... reasons.
the cromwell is a 90 fuel tank with a 20+ fuel fee for being british
The speed advantage that the cromwell (and any other similar allied tank) has is the speed, so naturally all the axis mediums you'll face have the almost exact same speed, and get a SPEED boost at vet 1, negating the whole advantage you might have.
But i have personally witnessed the doom of a ferdinand user whose army died before the heavy TD went to the frontline, coincidentally my cromwell was fully repaired and would rush behind the ferdinand, chasing it across the map and eventually killing both it and a walking stuka, ending the game. Maybe dissing the poor thing just isn't worth it