I share your cynicism.
While they may have been some passengers who wanted to travel by VC.10 when it was new I doubt that lasted once the novelty factor wore off as the years went by (Concorde is probably the only airliner to ever maintain its novelty factor).
In any case its not likely passengers had a choice once the VC.10 settled into service. Once a certain type was allocated to a particular route and in service in numbers large enough to have a constant pool of available aircraft to reliably serve the route, then most often as not the expected service would be as scheduled. There would have been times when 707s or VC.10s swapped for serviceability/availability reasons, but that would have been last minute changes.
I'm wary of Gardner as much as I am about George Edwards' VC.7 claims (I've much about the latter in various VC.7 threads).
A manufacturer never admits they designed a duffer. In 1966 plenty of economists/bean counters at Lockheed, Boeing, BAC etc. earnestly forecast huge fleets of supersonics by the 1990s. Look how that panned out....
I agree. The Boeing 747 was too much aeroplane for 1969 as well and nearly flopped and nearly took Boeing down with it.
A manufacturer could always build as large or as fast (or as small and slow) as they wanted, but if it didn't chime with what the airlines wanted/could afford/finance/lease then it didn't sell. And sometimes the airlines didn't really know what they wanted. Trident was tailored to BEA and flopped, Lufthansa took a punt on the unknown 737 Boeing was desperate to find a buyer for and inadvertently begat a commercial giant.