The Old Mixer wrote:
Nobody's disputing that literally, only the D was referred to as the "flagship" onscreen. But the extremely brief onscreen lives of the B and C leave plenty of room for conjecture as to how the Enterprise went from being just another starship in TOS to the flagship of the Federation four generations later. It would be extremely silly to assume that we know all there is to know about the service and missions of the B and C based on seeing only the first day of service of the former and the last day of service of the latter....
Certainly there's strong evidence to imply the B was the flagship, after all, it had the big launch ceremony with all the media coverage. I doubt that happens for just any new starship. And therefore the C likely is too, since both its predecessor and successor were the flagship.