Let's not forget that the contractor is not tasking these aircraft. Also, that when availability all goes badly wrong, as happened during the Colwyn Bay incident in 2012, when Valley were off-line and Prestwick then broke a winch, a third base turned out to finish the job and it all ended well.
Except in that particular incident there were 3 bases, relatively close together, able to provide mutual support. When Lec came across to do the job the ARCC still had Wattisham and Boulmer to hold the East coast - not under the 10-base solution.
We come back to the fact that no matter how fast your aircraft, it can only be in one place at one time and, with the way the flights are spread, will leave massive gaps which a 'surge' capacity will take a long time to fill.