Don't underestimate the power of coming home, getting based where you intend to live. Especially as the Scandinavian countries are very family friendly. People come home for that reason..
You might be right though that some good candidates are lost in the process.
SAS is not an expanding airline, hence no need for DEC. Seniority vs no-seniority, I have tried both. I favour seniority. But you should get in early, the earlier the better.