^^That's another unwarranted conclusion. It seems to be the day for it.
I still get quite a bit of Southwestern European despite the fact that I get a lot of North Italian. It has nothing to do with any migration from Sardinia or Iberia.
First of all, there was never, until very recently indeed, any migration from Sardinia to the mainland. It all went the other way.
There is also no migration from Iberia to Liguria or Emilia.
In my own particular case, I can trace my ancestry back to the middle of the 1500s, and on some lines back to the 1100s and 1200s, and there is no such gene flow. In my father's case, in particular, all indications are that they were up in the northern Apennines by around 1000 AD.
Part of it, in the case of Liguria or even nearby areas in Emilia, may be attributable to Gallic migrations of the first millennium BC. There's a reason these people were called Celt-Ligurians. It is clear from Gencove's map that South Western Europe doesn't just include Iberia. It also applies to the southern half of France.
In addition, I would propose that most of northern Italy was once probably "Ligurian like". One of the differences is differential impact of the Lombard invasions. Yes, every hill in my valley is crowned with a Lombard castle. However, they entered through the northeastern corridor of Italy, and the density of settlement is strongest there. Also, the Lombards seem to have incorporated other men and women as they moved, so they may have been different by the time they incorporated some parts of Northwestern Italy.
Drift due to long separation would also have added to the structure.
In this calculator North Italy is centered on Northwestern Italy plus Tuscany.
As for "relatedness", we all know or should have known that Davef meant genetic similarity.