lol, I agree, it is a bit off topic, but it helps the topic immensly lol. At one point all of England and Wales (and we can assume Scotland) was Prydain and the people were the Cymru, the Goidelic (thanks for reminding me of the spelling there lol) arrived later. As far as I know it's common knowledge that the Scots and Irish came from Spain & Portugal and apparently Madeira too.
The four Celtic agricultural festivals, or "fire" festivals as people call them these days, have Irish names so yes it is a good point to question whether the Welsh did indeed observe them, considering that the Irish and Welsh spent a long time at war lol, but if we travel to other places that are definately Celtic, such as Germany, the same festivals are there too, and the Norse have them so one could (I assume, but knowing the Brits we probably didn't because we're too damn proud to be the same as other tribes) assume that these four festivals (Samhuinn, Imbolc, Beltane & Lughnassadh) were indeed practiced here. Beltane is definately a more "Brythonic" name than Goidelic comeing from Belenus or Belenos which is definately P Celtic. Lol, if we travel even further to the Buryat Mongols they have festivals very similar to those that we celebrate now as "Druidic", and even further too I expect and this is why I call Druidry a Shamanism. But in that I myself am forgetting that in truth there is NO set pattern of ceremonies in a Shamanism, they lie only in religions, so we need to be looking at something older perhaps than druidry?
Perhaps we celerated the first day of spring with the return of the Geese? what we now call samhuinn could have started as a fetival to celebrate the mating season of the deer because we knew that it would provied us with good game for the next year? Who knows?
This discussion is really exciting for me and I love this kind of debate