Never knew Jet2 had summer bases in Spain, until I read the above. Sounds similar to what easyJet are doing in Palma, having a few aircraft based there for the summer season.
I struggle to see the benefit if the Palma based aircraft is flying to existing bases, which could operate from the UK bases to Majorca.
Sounds like a perfect opportunity for Jet2 to operate to other UK regional airports where they have no base. Maybe like Humberside, Southampton, Cardiff, Exeter and Norwich, operating 1-2 flights a week.