Face it, it's all just rock n roll. metal, rock, punk, grunge...Whatever.
Led Zep were also classed as being 'metal' at the time. It doesn't make the description right.
every band mentioned in this thread will likely have an eclectic mix of influences and very few of them can be classed as highly original artists. Most of them will draw influences from early blues, early rock n' roll, Psychedelia, and country and western.
Sabbath never invented metal, they are just part of the evolution of guitar based popular music: Adding their own elements to many influnces that had gone before them.
It's a very grey area, but I'd cite Judas Priest before Sabbath.
There was a Classic Rock article a good few years back and there's shit loads of bands who were influencing the 'metal' sound in the late 60's, whom, for one reason or another, never became well known outside of their peers.