Couple of points occur to me reading this thread.

a.) Staffs exist to enable Command. That's it. That is all they do. No Commander, no Staff. You don't need staff to support any activity you do not directly command.

b.) Yes staffs are too big. They have been since about the 1950's. Most of what staffs do is utterly irrelevant, to the exercise of command.

c.) Why should a staff for a so-called COIN operation be any different from one concerned with Combat Operations? Command is Command. All the military functions are the same.

...yes I know there are lots of human, social and plain ego stuff that gets in the way, but progress comes from realising it.