Seeing alot of metal on the ground on a Sunday morning isn't unique to either Jet 2 or LBA! Alot of UK airlines operate 'slack schedules' on Sundays - particularly in winter.
I have to admit though that Jet2 have, up to press, always kept alot of capacity in reserve. Their first full Winter was always going to be an unknown and prudence seemed to be the name of the game. This summer should see that change, however it appears that slot availability has put a block on some 'nice to have destinations' - there appears to be some spare capacity in the programme.
Tonight though (Sunday) for Jet2 sees at least 4 of the 5 units earning their keep with arrivals at LBA as follows;
LS266 MALAGA 2010
LS294 BELFAST INTL 2050
LS206 AMSTERDAM 2130
LS198 PRAGUE 2155
...and I'd reckon that with the exception of possibly the BFS those flights would be fairly full.