I spent three years in the ARRC and I agree that the multinational corps is an excellent tool for building cohesion among allies. It is also an excellent way to expose small armies (such as Canada, UK, and Denmark) to work at the three-star level...more important for their majors and lieutenant colonels than their generals, in my opinion. After all, every European country that today can barely muster a palace guard has, in the past, fielded multi-corps forces. Corps is probably the best and lowest level at which you want to construct multinational staffs. At lower levels there is too much friction created by day-to-day operations with actual soldiers and equipment. At higher levels, national politics begins to become a real problem and...to be brutally honest...in NATO there is little constructive work that can be accomplished at echelons-above-corps.

The only caveat is that, with no units permanently attached or assigned, the headquarters tend to be onanistic and unfamiliar with the friction of everyday operations