Please note that the comparison with Ostheer vehicles is a bit flawed as the Ostheer vehicles are lacking for cost.
The Ostheer 125 fuel Panzer IV loses to 110 fuel Cromwells.
And 135 fuel SU-85 loses to 90 fuel StuG.
230 fuel Pershing loses to 175/200 fuel panther.
AEC loses to a pair of 222, which cost over 50% less fuel and similar menpower.
Your point?
The Ostheer Panther is regarded garbage by many except the Allied fan-train. It can´t engage cost efficiently.
The sole problem with ost panther was how late and costly it was to get it.
Now, go ask Hans for example about the panther and hear the opinion form someone with a clue.
The OKW vehicles can actually fulfill their role due to better stats. That doesn´t mean however that they are cost effective. They both come 25 fuel more expensive to fulfill a role that the vanilla Ostheer vehicles should fulfill but can´t. This means you are stuck with either performing vehicles for a too high cost or weak units for an average cost.
You can't look at OKW med and heavy armor costs the same way as you can at other factions, OKW was supposed to have lesser armor presence in comparison to other armies, the extra 25 fuel on T4 and call-ins was to keep that goal as december revamp have proved that OKW without that pumps armor way too fast.
If you want to look at cost performance of OKW armor, then you need to take away that 25 fuel extra, because it DOES NOT contribute to cost effectiveness at all, but is a timing and numbers limiting factor EXCLUSIVELY. This is precisely why OKW armor wasn't buffed to ROFLSTOMP everything and anything after the price increase after dec revamp.