It depends on the country. For instance, the three leaders of the AGs for Operation Barbarossa were all Field Marshals, while Franz Halder, the effective commander of the theater, was just a General.
And I think that the current system can do a really playable representation here - a battle-plan each for the North, Center and South, and then pool reserve armor under your favorite Panzer Leader as extra weight to throw into areas being stubborn. Enough plan options to coordinate multiple forces, and the ability to choose abilities for wide swaths of front, without having effectiveness be strongly impacted by micro details that a player will
always be able to coordinate better than the AI, but only at a high micro cost. Because that's really the thing about stuff like Div commanders - either they have minimal impact, in which case there's literally no point to having them as a player touched thing, or they do have an impact, in which case there'll be serious outcome differences in the same plan depending on whether you bothered to spend 30 (or more!) minutes manually assigning all your officers to 100+ divisions. If I'm being asked to be Halder,
I have staff for that. If I'm being asked to be Hitler... well, sign me out of that personally, but then I would
really have people for that.