companies such as monarch are more likely to get a superior product at the end of a heavy check due the fact their engineering division is i believe one of the finest in the world, and they are working on "their " aircraft, so people tend to go that extra mile , no doubt the eastern european company who look after jet 2 do a reasonable job, but to them jet 2 are i would suggest just another customer,
I have to argue with your logic:-
The 'Eastern European Company' are a contractor to Jet2. There are other contractors who would happily do the work. Therefore they cannot afford to do a 'reasonable job' they have to do a good job or the work will go elsewhere.
The Monarch Engineers get paid whether they do a good job or not. They are no more likely to go the 'extra mile' than any other engineers.