I was never arguing that Zeppelin were not influential to metal, they were, along with Hendrix, however neither artist was metal. Dont tell me to read up on the history of music or tell me how rock started. Just because Led Zeppelin were harder then the other bands at the time does nto make them metal, they are not metal. Black Sabbath were of the same era as Led Zeppelin, neither really predate each other. Black Sabbath brought to rock music more of what is considered metal, detuned guitars, the dark lyrics, the stage antics. Whether people play it faster or slower, forwards or backwards almost every cool riff has been written by Sabbath.
It was also Sabbath along with the likes of Priest and a lot of the acts that came about in the mid seventies such as Motorhead, Def Leppard and Iron Maiden which led to inspiring the Bay Area thrash scene and contributed to the overall rise of heavy music in many parts of Europe as part of the highly influential NWOBHM scene.