I recommend you read Stephen Oppenheimer's new book, "Origins Of The British." He has some very interesting DNA data on the Sa'ami and their origins. Very technical but informative book.
The Gaelic speakers had earlier come from the Danube through the Black Sea, and around the Mediterranean.
One imagines this having been the regular route for a single group of sea-faring Gaelic speakers.
For a variety of reasons the Iberian records, which are far older than those used as a basis for the King Arthur material, have been rejected by English archaeologists and historians.
The part of the ancient stories that relates to King Solomon has received the harshest criticism.
We have a far more recent example of Gaelic speakers flowing into Iberia that is nearly as forgotten. King San Cho Noe I came to Galicia from Cornwall and conquered the remaining Gaelic speaking and Visigothic kingdoms in the area. He reorganized the order of life and initiated the Reconquista which ultimately re-Christianized all of Spain.
Lebenteenzillionpercent of everybody think Sancho is Iberian in origin.