"If most of EUJet's flights were operating at near capacity, and the only reason for its failure were the 'highly paid staff', why is it that Ryanair and easyJet aren't beating a path to Kent International's door?"
How do we know that they're not? Infratil are very well in with Ryanair, but my information is that they don't want to become too dependent on them. Both of these airlines have a long lead-in for allocating aircraft, particularly when deliveries have been interrupted.
"Everyone else in the industry knew exactly what would happen. Wrong aircraft, wrong business plan, wrong airport. Like so many other professionals have stated since the 1960s, Manston has no catchment area, no surface links, and therefore no real future as a scheduled service airport."
Who are these experts? If they have been stating this since the 60s they would have started at the time that Manston had a lot of passenger traffic.
"Perhaps one day when a motorway and rail link are built, but certainly not now." Have you heard of the M2/A299 connection? Have you heard of the CTRL being used for domestic high-speed services from 2009?
Manston is not a London airport; it's Kent's regional international airport. EUJ did pick up a lot of custom from SE London, but most of the traffic was from Kent and Sussex.