I haven't checked it recently but don't the Sherman's AP shells have the same penetration profile as the Cromwell?
Penetration values don't tell the whole story.
The Ostheer Panzer IV has 180 frontal armour to the Cromwell, Sherman, and T-34/76's 160. The Cromwell, for example, has the same chance to penetrate a Panzer IV as the Panzer IV has to penetrate a Cromwell at point-blank range (75%) but the Panzer IV has a slightly higher fire rate so it is expected to win head-on fights. At any other range, the Panzer IV has a higher chance to penetrate the Cromwell than vice versa (M 68.75% v. 66.66%, F 62.5% v. 58.33%).
The T-34/76 was fairly widely considered a poor tank before the MG buff despite its low fuel cost because the penetration fall-off meant it was extremely unreliable at any range but point-blank (and it couldn't reliably kill infantry).
The problem with major buffs to the penetration of any medium tank is that they devalue both more expensive and heavier-armoured units, and tank destroyers. For all the issues players have with the Tiger's "low" frontal armour, your average medium tank has less than a 50% chance to penetrate it.
I've spent a lot of time testing the P4 against other mediums at max range and at killing infantry. I can't understand why the price is as high as it is considering the P4 doesn't perform in either aspect any better than the price would suggest.
You not taking scatter and moving accuracy into consideration.