The big deal is who lives in these places now, and what they think. The peoples who were there at one time don’t matter. The past is past.
Half my family is Basque, and were Basque nationalists. One of my great uncles was a member of the Basque government in exile. I understand the situation of Ukraine very well, our position was analogous, vis a vis Spain. The Ukrainians insist on independence, and they should have it.
Unfortunately for Basques, they didn’t have a big brother next door. If France was majority Basque, it would have annexed the basque area of spain ages ago