Hmm!
OUL-ARN doesn't exist anymore. There aren't any more regional flights to CPH, but Turku sustained the flights longer than any other regional airport. Turku still has low-cost flights during the winter period (TKU-GDN) so the Tampere preference isn't quite true.

I browsed SAS flights to Arlanda during February. Both Turku and Tampere have four flights a day, however two of flights to/from Turku are operated by 737 where all of the Tampere flights are operated by ATR/SAABh