Well actually it's Athens although Melbourne may well be third. Look back at the census returns for the beginning of the twentieth century and the town with the most heads of household born in Radnorshire isn't Rhayader or Knighton and certainly not Llandrindod. Infact it was Merthyr Tydfil.
So while some might see Radnorshire as a rather fey, in-between land, a place which incomers can safely colonise without having to rub shoulders with prickly North Walians or perspicacious Southerners, the better-informed will know that the county has always been part and parcel of mainstream Wales.
Back to the song. In the 80s you'd often find it on jukeboxes in South Wales pubs. We used to play it - much to his annoyance - for a workmate from Tylorstown. There are not enough Welsh songs in English. It never bothered the Irish but in Wales I think there's been a tendency to think Welsh songs should only be in the Welsh language.