Its swings and roundabouts, Jet2 aircraft are old (and getting older) and even with the best engineers in the world and the part support with it they will go tech more often than a new airframe, on the other hand Jet2 are generous with their luggage allowance compared with Ryanair, but you would be amazed how few pay attenion to that until its too late.
Leeds has long been a cash cow for Jet2 and they have opened Leeds up, but people want low fares and Ryanair don't get much lower, the only way MOL can make use of the massive over supply of seats/airacraft ordered is to see off other airlines and this will hit Jet2 profits.
If the goverment ever grow enough balls to part-privatise the Royal mail then Jet2 will get a bigger shock if DHL become part owner of RM
The selling of seats to other tour operators is all well and good for now, but if they come to rely on that business they will leave themselves further exposed.
Ryanair wil within 18 months probably have more movements in/out of Leeds than Jet2 unless Leeds has a very snow/foggy winter for which LBIA have not invested in, a 40 year old unimog snow plough is not what MOL will expect.
The best Jet2 can do is to be different and drop this one bit of hand luggage nonsense, flying a half full 757 to ALC won't make money and they will never drive their staff cost down to Ryanairs level
Time will tell, but good on Leeds for getting a new player