Recent paper on pictish genetics:
In summary, they still don't know a damn thing. Just not enough bodies to study up there I guess.
The Scythian origin story is cool. They arrived via ship from the steppe, coming through the black sea -> the med -> Gibraltar and up the coast. It was all men so they stopped in Ireland and the irish gave them wives, but insisted on inheritance from the female side for the kings.
Scythians were intensely patriarichal, so not sure how or if they convinced them to stick to that idea. They think the wives may have returned to ireland for burial as well, further muddying the genetic waters and ability to study graves of elites.
My guess is the wives were considered elves, which is a big boost to a king's royalty score. I suspect some of the elves in the scandi kings lists were just irish women.
Edit: Can you imagine Scythians without horses? Also if you think about the path of the journey, it would make more sense that they paid for passage north. Maybe they were an exiled tribe running from justice. They could have easily paid the Phoenicians for passage in gold as the Scythians were loaded with the stuff and the purple people were sailing often to the british isles for tin.