The no-mixing part is what got me. If "viking" was just a job open to anyone, you'd expect genetic mixing in the burial sites. But Swedish groups went east, Danes south, Norwegians west — distinct genetic clusters throughout.

So it was a job, but one you apparently got by being born in the right place

Don’t take “job” literally. It wasn’t centralized in any way. It just meant if you had the resources you could build a ship, hire some henchmen, and go raiding. It is not surprising Swedes went East, Nowegians Northwest etc - just look at a map.