That is rather inaccurate:
PzIV Penetration near 125 Penetration mid 115 Penetration far 110
Sherman Penetration near 140 Penetration mid 130 Penetration far 120
Cromwell Penetration near 135 Penetration mid 120 Penetration far 105
T-34/76 Penetration near 120 Penetration mid 100 Penetration far 80
(Things get even worse when it comes to penetration if one compares PzIV H to allied premiums.)
I most cases allied mediums have better penetration.
My Sherman pen goes 140/120/100.
But apart from that, the raw pen value is pretty misleading. We should compare pen chances against a certain target, for example against other stock mediums.
OST P4 has ~70% pen chance against Sherman/Cromwell at range 20, it's 65% the other way around. The bigger the range, the better the P4s perform, at lower ranges P4 and Sherman/Cromwell become pretty much similar (all calculated with "my" penetration stats of Sherman).
This system sounds alright considering the slightly lower price for Sherman/Cromwell.