Cromwell is cheaper, is 50% more accurate on the move on top of having higher base accuracy, extremely good at crushing, faster (and gets ludicrously fast with vet), has a smaller target size than any other medium tank, comes at a significantly lower tech cost, has nondoctrinal smoke, and has a gun that's noticeably better at penetrating other medium tanks.
P4 starts to come into its own only after vet 2, and that's only against other medium vehicles and infantry AT weapons. Cromwell is by far the superior vehicle for cost.
Amen brother.