It depends on a variety of things - pricing timings etc.
Ryanair are predatory at STN- it is heir heartland and they will take on anyone where they perceive they can make money and potentially out compete. That's the way a market economy works.
I speak to lots of folk who think Easy should have stayed there including a pilot who works for Easy. They are I am afraid wrong for as long as it is dominated by Ryanair.
Does it matter as long as STN is connected to GLA and EDI?