As big a boost as it is for Bournemouth, the frequencies offered by Jet2 from there aren't massive.
Still plenty of potential growth for easyJet out of Southampton. I don't see it necessarily as one or the other....yet. However, I'm not sure they can afford to give Jet2 too much of a head start as they're a very canny, very well run operation and will no doubt will flood the local radios etc with marketing campaigns.