The key is maintenance, in my opinion. Jet2s fleet is double the age of TOM and TCX but they seem to be having half of the problems.
Whether that's there stand by aircraft procedure or maintenance schedule, I don't know, but they've had an almost faultless summer.
Not to mention they're extending bases, adding destinations and still making a lovely bit of profit! They're probably the envy of most airlines right now. Them "old and knackered" aircrafts are doing what Jet2 want them to do at the moment. Make money.