The Irish language is closer to the celtic that the celts used to speak in Iberia (pre-Roman / Arab invasion) than to the celtic that the celts spoke in France, if that makes any sense. I learned this on wikipedia.
Also in terms of genetics the irish were a mix if Northern Spaniards and the Scots, before the Normans, Brits, Vikings and Romanians started arriving and bastardising us.
It’s my understanding that our genetic relatives in Spain are more the Galicians than the Basques and Basque is of course Europe’s only language isolate. Perhaps a glimpse in pre-Celtic, stone-age Europe. I would suspect that the Basques like to believe in the irish connection in part because they feel lonely but belief in it goes back to pre-famine times when people thought that Irish was the oldest language in all of europe and related to Basque. Today we know that’s not true.
I remember seeing an interview with the English historian Niall Ferguson and he was very arrogant. He addogantlybsaid that the irish were descended from the french but the evidence doesnt support that. He didn’t know what he was talking about.
The idea of a a stone/iron-age Spanish invasion if Ireland is something that I find very inspirational. Was it political with a great King organising it or was it a spontaneous cultural thing? We’ll never know.
Of course it’s very possible that at the time the Spanish started moving to ireland they were all in France at the time and they migrated south into Northern Spain later on, taking their proto-Irish with them. But that wouldn’t really change anything, we’d still be descended from the Spanish.