Gulliver, that sounds a bit like Wolf Maahn, who was a pop star about twenty five years ago. He did an unplugged tour about twelve years ago.
BAP did sound pretty vital in their early days. They had the idea of doing very topical songs in the Kölsch dialect. It certainly caught on in Germany in a big way for a while, but BAP are only a medium level band now.
They were friends of Wolf Maahn, of course. Maahn is originally from Berlin, but they are both Köln based.
The connection of either band with folk music is pretty tenuous, however. Klaus (der Geiger) did appear on one of Niedecken (of BAP's) solo albums. So I guess Nidecken got a little "folk music" credibility out of that.
You can't really compare the German music scene to the UK one though, because even in rock - let alone folk - the regional differences and dialects are so much more important.