Complex sentence: Deep Purple are cited as one of the pioneers of hard rock and heavy metal, along with Led Zeppelin and Black Sabbath, but Deep Purple was never as famous as Led Zeppelin or Black Sabbath.
Split into simpler sentences: Deep Purple are cited, along with Led Zeppelin and Black Sabbath, as pioneers of hard rock and heavy metal. But Deep Purple was never as famous as Led Zeppelin or Black Sabbath.