It's pretty obvious to me that Black Sabbath and Judas Priest are metal. The sound that defines those two bands unique sounds define what metal is. Sabbath was the Groovy Doom, Priest was the Neo Classical Proto-Thrash Riffage. Zep and Purple are pure Rock and Roll. The have their metal moments, and riffs as did Rainbow, Rush, Blue Cheer, even the Beatles... But Sabbath and Priest were Metal Bands. Even the weird early hippie stuff lol.