As mentioned the VC-10 was built for "hot and high" performance out of very short runways on BOAC's African network. Hence it had a very large wing for its size and very powerful engines. It was not, therefore, very economical to operate cf with a 707.
Unfortunately for Vickers the governments of these African countries, worried that 707s and DC-8 which could not land would overfly them, spent fortunes extending their runways hence removing the market for the VC-10.
The VC-10s economics were improved with the stretched Super but the drag from the large wing was always a fuel penalty.
Vickers/BACs marketing was not helped when Boeing obtained and published an internal BOAC document comparing the Super VC-10 and the 707 which discussed the higher fuel burn of the VC-10. Of course, Boeing did not publish the bit which followed which stated that, when operated on a route in competition with other airlines flying 707s and DC-8s, BOACs VC-10s carried, on average, 10-20 more pax - because pax wanted to fly on a VC-10. The increased load factor more than compensated for the extra fuel burn!