I do not have a Centurion card, but the pattern of complaints I read here suggests that the artificial distinction between...

Customer Service
Travel Agent
Concierge

...is a core problem, aggravated by the apparent outsourcing of two of these functions. Is it too much to expect that one American Express employee could be trained to perform the Customer Service, Concierge and at least routine air/car/hotel booking functions? I can understand needing to deal with a "specialist" if booking a round-the-world airfare, cruise etc, but otherwise it seems Centurion ought aspire to approach the same level of integrated service that you would obtain if you hired an assistant.