I guess the Armada theory is just more sexy which is why people like to tell it and why it persists.. (its not as interesting to say the 'black Irish' are those with black hair, or possibly from the Basque connections.)

I had no idea it was debunked.

Regarding the Celts in Europe - In my birth country Czechoslovakia
prior to 600Ad it was mainly populated by the Boii celtic tribe
(hence the name Bohemia - home of the Boii)
IN my home town Tabor they found a bronze celtic boar kancik
in 1869.

Celts were found as far east as the western desert of China
(The Tocharians) I remember seeing a NOVA episode a few years ago
during the burial excavation they found Tartan cloth.