Did the Greeks ever adopt foreign equipment ..

[Robert Vermaat]

Say, the tube and yoke armor. It was ubiquitous among Celts, until mail came along. Should we assume the most numerous people in Europe, renowned craftsmen, adopted Greek equipment on such a scale after encountering a few Greeks?

I'm not so sure where this model came from that the Celts encountered 'just a few Greeks'? The Celtic world was not limited to Gaul, but stretched into the Balkans and all the way into regions long influenced by Greek culture. Celts were mercenaries in many places also colonized or influenced by Greeks. So if they indeed adopted the tube and yoke armour, then why not from any of these places? Chances aplenty, I'd say.