Volks are cheaper, they are not better. One has to be braindead to let 4 volks advance across open cover past 4 tommies and a suppressing bren carrier, then eat a flame nade, and then eat a spec ops nade to loose a squad.
Also it is a bit weird how two vehicles with more expensive tech (with lower starting resources) might be better than one vehicle, hmmmmm I wonder why.
Volks are good because of their cheapness and utility, and five man StG volks beat four man 280mp vanilla Tommies. Even if your in green cover or a house they can run up and flush you out with flame nades.
Which is why in current meta bolster is so popular, and my exact point...
With Brits you are juggling some awkward micro of Tommy+WASP+royal engie to get the same tools that a volk has stock for free.
If you're going to delay IS combat upgrades without giving them missing tools, playing OKW vs UKF will be a walk in the park.