then u didn't actually calc it, with their minus starting fuel and all upgrades unlocked okw has the most expensive full tech tree (even more expensive than ukf) and tank will come later than other factions unless they buy side techs (example ukf reach tanks rushing by 50 less fuel than okw with upgrades like bolster and weapon they even out, usf is similar )
The FU gain for each faction to rush their medium is (USF has ambulance upgrade included as they have no possibility to heal otherwise):
SOV/USF/UKF/OKW
255/275/235/310
Now the OKW tank is the best stock medium in the game, it's fair that it is better. we can adjust this by correcting for the fuel price difference, which leaves us with:
305/305/265/310
We can see that UKF can rush a medium super early, but usually they need to bolster in the early mid game since IS fall quite far behind performance wise if they don't get boosted in some way. This adds 35 and brings them up to 300.
So the performance corrected needed fuel gain between OKW and other Allied factions has a difference of 5 and 10 fuel, respectively, 45 (which is quite a lot and an equivalent of about 2 min) if UKF does not bolster. To get the full options that OKW has (weapon upgraded main line inf, nades) UKF needs to pay 325 which is fair as their bolster and weapon upgrade give them slightly better options (additional MP cost fully neglected here and down below, too).
If USF side techs, they exceed OKW, which can be almost equaled out if OKW side techs medics.
Now, there are other soft factors such as (Volk opening) OKWs early strength that allows them to get more resources relative to their opponent.
There's no reason to say that OKW pay more for their stuff.
EDIT: I mean then it's fair to add 15 FU to OKW for the medics as well, as the Allied factions have it at that point. Brings them up again to USF/UKF levels. Only SOV have the ability to get full tier and medium for less fuel gain than OKW by (medics included) 20 fuel.