I sort of agree with you. The way I see it, the only thing that we lose by abstracting the HQs is the HQ range mechanic. As it is now, troops in far away lands will only have the benefit of a corps HQ, since it is too costly to build army/army group/theater HQs for them. Using an abstracted system, I can't see how that range/cost mechanic could be kept.Now let me ask you this... is it really necesary to show dozens of units with no combat value whatsoever on the map and force the player to move them behind his troops and take care not to forget them and let them be overrun just to show some sort of command structure? Wouldn't it have been easiert to have a nice command level tree in some interface screen under an additional tab which lets you organize that, maybe a button in a unit that opens a view of its siblings and superior HQs and keep the map reserved for the actual fighting units? It was already ridiculous in HoI2 to have several HQ units on the battlefield and even have the AI attack you with them sometimes but now you have dozens of them and none of them are there to fight, they're just there to hold a general's chair...
On the other hand, the gameplay benefits of an abstracted system might be more valuable.