Black Sabbath, while clearly a heavy metal band, definitely had a lot in common with the blues-based hard rock bands of that area, much more than the style that Judas Priest would develop into by the late 1970s. I also stated that some of the bands in that part are heavy metal bands by right. It's still clear that Judas Priest moved forward in a way that Black Sabbath did not.
Queen is also a pretty underrated influence on the development of heavy metal as it lost the blues influence, as cited by Judas Priest, Iron Maiden and other bands that began to play metal at this time.