....
For me the kubel should fill a mostly scouting role - hell I wouldn't mind if the price was lowered and it's offensive capabilities were removed and its health nerfed
slightly and in exchange it gained more speed, maneuverability (because it always has handled like a shopping trolley) and scouting ability.
The faction doesn't need all that early firepower AND capping ability. If this happened, the Kubel could be used as an early game scouting unit that allows the OKW to know where their opponents are going map-control wise and place their HQ's accordingly.
I don't necessarily agree that the flak truck needs to be a purchasable upgrade but repairs, healing and shrecks should be. If this was the case the OKW would have to be more cautious with their truck placement, in the early-mid game anyway and the kubel would be the ideal unit for making sure this happens. rather than just capping the rest of the map while a squad of pios and volks hold up your army at your cutoff