It was not "his band". Although Ozzy was in Black Sabbath from the beginning, he was enlisted by Bill Ward and Tony Iommi together with Geezer Butler because as a drummer and a guitarist with a vision they needed bass and vocals with them.
Ozzy was kicked out in 1979 and started his solo career in the shock rock tradition he is mostly known for. The idea that sparked Black Sabbath however was a heavier blues than ever heard before and that was Ward and Iommi.
As you say, they were some of the originators of heavy metal. There is no single inventor of the genre. There never is. Culture is cross pollination and collaboration.