Not only simultaneously and sequentially but in rotation and in varying theaters with little reset time, even a direct move from one type in one area to another type in another nation. That and the distinct possibility that one can be confronted with no IW, just pure short sharp conventional combat for months, even years, on end and then suddenly have to pull out the COIN book and vice versa. All sorts of permutations and I'm not sure we're ready for it. We can cope, we generally do but coping is less than adequate...
A great description!

One contributing factor to this is our continued attempt to be fair and equitable and to produce interchangeable leaders and staffers. Schmedlap addresses that HERE (note particularly his 1. and 3.) and HERE.
You point directly to a central problem, if not the central problem. That the system itself serves to mitigate against success is a problem that has been articulated to me by others over the course of my research. Schmedlap’s poignant observations identify a particular set of serious issues. Sadly, it would take a substantial change in the culture of the military just to adequately address his (and others) concerns……

We are a professional Army with some really sharp people at all grades. We ought to be able to do that and a few units can. The Army must be able to do it. That takes agility.
I agree that ultimately it is the entire service (and this includes all the services, not just the Army) that needs to be agile – and therein lies the rub. Whether it is even possible to transform the current organizations into agile ones is the great question, and I have real doubts about whether it is realistically possible.