I don't think Ryanair or Easyjet is the real issue
The issue is the lack of airline choice at Liverpool.
How popular was Shannon at Liverpool? If it was, perhaps 1 of the 4x Manchester Air Lingus services that are leaving to be replaced by the 1x larger Ryanair flight can potentially move to Liverpool
Theres various routes such as Gatwick which Manchester lost, Cardiff. Bournemouth etc that Liverpool could gain domestically
As for European perhaps Blue Air will add more destinations in the future