what aces?
Shed, Ryanair have the benefit of size and maybe cheaper airport fees for awhile. Jet2 has 1st mover status, ie they have existing clients, some degree of loyalty and know the market well. With so many based aircraft they can arrange their flight times to better suit the pax. Their old a/c mean that their cost base is probably lower than Ryanairs, especially when you consider that they are more diversified, selling seats to tour operators, flights for royal mail, a large charter operation and a holiday company.
Ryanair may well not want a bloodbath, for the reasons I've outlined above. Just because they have a few aircraft based doesnt mean that there will be two dozen soon after. They simply want somewhere they can operate and be profitable and I think with LBIAs large catchment area there is plenty of room for both.