If you've been told to work on something else, and you get a call from the customer asking about project status, the correct answer should be to refer your customer up to their allocated project/account manager.
If your boss is re-assigning you then not keeping the customer informed on progress, that sounds like bad management, not a flaw in the agency model.
In that particular case my manager would not have done anything different than I would do or get any different results, it would just be somebody else doing it.
Effectively I was doing the project management and the only thing he was doing was cashing and cutting checks.
If your boss is re-assigning you then not keeping the customer informed on progress, that sounds like bad management, not a flaw in the agency model.