Just to add my opinions....
Lack of credible back-up is normally reason for a delay such as 7 hours if original aircraft not fit for purpose.
This summer Thomas Cook will have an A320 as a standby aircraft 6 days of the week and an A330 for May / June / October! So they do have back-up aircraft. Also, it is not always the fault of the airline that there are delays...take the other week when a set of stairs caused damage to a TC aircraft. This is obviously something outside the airlines control!
just a shame he used TC as I also have never departed on time when flying with them!
And I have never departed late when using them!