Did Ryanair not used to operated to Birmingham to Oslo Rygge
I believe they did, but it would be wrong to compare a Ryanair service to a typical "Ryanairport" miles away from the city it's supposed to serve, with no infrastructure, and no viable connections with a FlyBe business orientated service to a city's principal airport.
My gut feeling is that OSL will do well for them, and it's great to have an airline serving both the business and leisure traveler to, and just as importantly, from the Midlands.
If the much expanded BHX network proves to be a success, then I'd bet that Easyjet would wishing that with hindsight they had invested in the airport - but their loss is most certainly FlyBe and BHXs' gain.