I think alot will eventually come out in a book or a movie because its a dynamic story. From what I've gathered, Sharon grew up in the music business and was not really on a path to 'inherit' any kind of piece of it. So when she bonded with OZZY she had some serious insight. She knew how musicians were, and probably had to have a filter to deal with them with all the drinking n drugging and eratic behaviours. She also knew Ozzy was a huge risk, personally and financially. Lets be real, nobody knew how long it was going to last with him. So Jake got an emotionally charged, your all replaceable attitude.
Zakk on the otherhand was completely different. Ozzy saw a childhood picture of him sitting on the steps of a house and had feelings evoked. He asked who that was, and a one in a million chance it was Jeff, to become Zakk. He was recomended on top of it by Mark Weiss the photographer and it was down to him and Jimmy Bell whom was left handed and dark haired super shreader like Yngwie in many ways. So, the band bonded with Zakk first, Sharon bonded with Barbaranne, Zakks high school sweetheart and later wife and Ozzy was already decided. The funny thing is his audition tape was weak. He was so much better live in N.J. So when you go back and watch Zakks Pentatonic Hardcore instructional, he is a Beast. And that style is from him deciding to not tread on certain things :
Just bypass the getting up to speed beginning and head half way in :
Funny stories : he decided to grow the beard on the Rockstar movie set. In the closing scenes he was wearing the beard and afterwards decided to give it a go!
When he put out the Black Label Stuff, Ozzy was like , " Zakkie, I don't want to be the Lead singer of Black Lable you know " . So it was a mutual realization. Not really a firing. Sharon went on to have Barbaranne as her understudy to the business when this all stared so she is very involved.