Hi Galaxy68,
Ryanair don't do peaceful co-existence with direct competitors. It is (sadly) fanciful to suppose that they will not target the Jet2 customer base from LBA. Where Jet2 has built up a market, Ryanair will be very happy to cannibalize it, and Ryanair know that many leisure travelers are not brand loyal. As you suggest, Ryanair can expect to pick up some customers who would otherwise fly from neighbouring airports - they are fair game too. But Jet2 has a bloody battle on its hands at LBA, be under no illusions about that (PM won't be). And Ryanair is holding the aces.
Cheers, SHED.