Memes

That's not really a culture of colonizers even during the height of Ancient Erin. A possible analog for a past group that very well could be a stand-in for inter proto-Irish conflicts as much as inter Gaelic ones is so tenuous at best. Most cultures have something like this, and it would be tantamount to saying there was an inherent colonial culture in the Ho-Chunk people because the Wąge-rucge man-eaters might be a cultural memory of another tribe their ancestors fought against.

There is a world of difference between human migration and conflicts arising therein and what we would identify as colonialism. Why even bring it up as such? Plus the Tuatha De Danann from even a quick search seem to be theorized to be Gaelic gods recontextualized into a post-Christianization culture. So it is literally not even from a culture of colonizers, but the reformatting of their own beliefs to a context of a cultural conversion. They seem to have come to mean "folk" or people much later and originally the term implied godliness. And then there is the PIE stuff and war between gods with humans in the middle which is foundational to a ton of places meaning it could either be remnants of a way more ancient myth shared with the Vedic and Norse etc, or a recontextualization of unique traditions subconsciously along the same lines as more eastern Europeans and Indo-European cultures. Least that's how I view the Iliad elements in Irish myth, maybe a shared tradition or more likely later writers put characters and stories into a structure they already knew, ie the most recited myth in Europe.

We really need to be careful with history and modern terminology/conceptions. Cultures did not really remove one another necessarily, nor can we accurately talk about Bronze-Age and earlier cultures in strictly defined terms. We use names given to types of pottery we find to describe a general human presence in a large area across thousands of years. It is broad and ambiguous on purpose. Hell even more recent cases like the Germanic "colonization" of Celtic England is WAY more ambiguous than previous historians thought.

For that history and a good object lesson on how complicated human migration is to decode there is a great video by CambrianChronicles on Brythonic Britons and how they never disappeared https://www.youtube.com/watch?v=5FHRTpEhaAs

And that's not to say that there was not a colonization and resistance in that case, far from it. There we have a material understanding of both cultures that can be defined even if the lines between the people of them is nonexistent in a practical sense. CambrianChronicles has several videos including one I LOVE on Arthur that drive home how originally Welsh/Briton Arthur was essentially a propaganda character for anti-imperialist movements. My point is the distinctions quickly disappear and framing there as being such a thing as "culture of colonizers" in a time when people hardly if at all identified themselves as having a culture is silly, applying it as far back as the etymological history and patchwork shifts in linguistic groups of the Bronze age is downright ahistoric. Especially with Celts, the very definition of which is hotly debated.

Another good POV is the short but wonderful history of the Bronze Age Collapse "1177: the year civilization ended" which shows some amazing research on how crises cause mass migration and why old models of how ancient Greeks came to Greece are pretty off base, with what was thought to be an invasion from the west by the Dorians might've been large refugee movements from Asia Minor which coincided with populations from Mycenean Greece fleeing eastward due to their problems. Heck the Sea Peoples are very possibly a phenomenon of various refugee crises and/or desperate moves by kingdoms we know for sure about trying to stay alive during what must've felt like an apocalypse.