Why would (multiple) divisional levels continue to exist?

[Adm.Lee]

Repeating the bit about command structures, training effective staffs and leaders is one of the hardest and most time-consuming elements of creating an army. Why throw away all those effective HQs? Now, I'm betting some of them go away, as some intermediate level HQs are folded into other structures. Maybe there aren't platoons in the companies, or squads in the platoons?

The flip side to this is that if I am a corps commander with three weak divisions, I have three (presumably) effective subordinates who can control their own portion of the field for me. If I concentrate them all into one division, I've probably still got the same area of operations, so I have to parcel it out into three brigade sectors, with the same number of troops. I haven't been able to concentrate anything at all.

That said, I'd be a supporter of the concept of concentrating some assets like artillery and armor. Say, in a given division, locating all of the remaining tanks in one battalion/regiment/brigade, to simplify the maintenance and control, as well as to concentrate for battlefield effect.