While I agree that the Cromwell is actually not that bad (from what I felt ingame it lacks a bit in the AI departement compared to the P4s, but I don't have much hard data on that, you seem to have more), the pen on the Cromwell and P4s is mostly the same. Especially if you keep in mind that the P4s and Axis tanks in general usually have more armor. So P4 has about 75% pen chance (slightly depending on range of course) against cromwell, while it's approximately 66% the other way around. Rest of the stats is absolutely comparable.
The Cromwell is a terrible tank and I'm actually not even sure what useful purpose it serves besides countering Pumas. It costs as much as a Sherman but is worse in every way, Bad AI bad AT.