Guernica was deserved desu, filthy commie. And Basques weren't particularly persecuted beyond that.
And I think the Spanish names have more to do with historical migrations than what you describe
Basque nationalism wasn't even a thing until the second half of the 19th century. Compare that with the Catalans who had a major revolt every two decades since at least the 14th century
If you have a Spanish last name, no matter how you cope with it, it most likely name your ancestors were Spaniards. There's no pure basques in Spain since ages, especially not in the big cities. If you venture in some deep mountain, then maybe the local sheepshagger are pure basques, but that's only them.
That's why the most hardcore Spanish nationalist until recently were all basques. Carlism is basically a Basque movement. That's why most Castilians nationalists can't bring themselves to hate Basques the same way they hate Catalans. Then Franco happened and for some reason you started to thought that communism was suddenly cool.
I mean even Ignatius de Loyola the most important basque in history had Lopez as his last name lol.
t. Mutt with some catalans roots.