Hmmm... I wouldn't have thought to make that link between Galates and Goídel Glas. And I'm tempted to think that Gaythelos (or Gathelus, or Gadelus) is just as close as one writing about Goídel Glas could get to a Latin form of his name, which would have been a necessity, e.g., for John of Fordun, one of the writers who thus wrote. (Cf. Saxo Grammaticus' Latinisation of the old Norse names in his Gesta Danorum.) Much more readily comparable is the Welsh word for "Irishman," which is Gwyddel. Your mention of Geta reminds me of Greek mythology, where we have a Geta as the wife of King Ammon of Libya, son of Zeus and Akakallis. But there seems to be no connection between this Geta and your Geta/Geat. Another character to whom both Herakles and British royalty are more famously linked, however, would be much closer to this. Alebion, whose name is also spelled Ialebion, Albion and Alban, was a giant prince of Liguria and son of Poseidon who was killed, together with his brother Derkynos, in Provence, France by their cousin Herakles. Alebion's descendants, same as those of the Heraclid Keltos, are said to have founded the kingdom of Britain, but Alebion also had a son Geatas, the ancestor of a Pictish tribe from whom the Geats were thought to be descended.