Another angle to remember is that by some legends Arthur is the once and FUTURE king. Perhaps when he comes back he'll develop a taste for DEVO. :)

Seriously, the thing I most remember about welsh audio video presentations, (of which I saw 2 in my travels) was the sense that they were of the past and the future and the quiet romantic threat that Snowdonia would rise again. You can take the reasonable approach that more modern music is equally valid as it simply prepares for Arthur's return.