A meaningful command level of ground forces should offer more than staff work and radio traffic.

Most combat units are most of the time not really busy - but usually some combat unit somewhere is very busy, if not in a crisis or overburdened by responsibility.
Does it make sense to allocate support equally among the combat units (or formations - it doesn't matter this time) in light of this? Certainly not. At least some support and some reserves are being pooled and under direct control of the superior commander.

A commander with only staff and radio guys would have no direct control over anything but the combat unit missions. He could not create a quick Schwerpunkt with the direction of his support assets (electronic warfare, engineers, artillery, area AD, nbc troops, and much else).
Meanwhile, his combat units would need to be designed for almost worst case scenarios because they couldn't expect non-organic support from a higher level.

A level of command without substantial direct assets (other than combat units/formations) for use in their whole area of operations is therefore systematically inferior to the same level of command in a force which balances its support between decentralized and centralized control.
A very lean divisional or corps level with staffs and signals units only is a suboptimal decentralization extremism version of force structure.