Ronnie's mistake was ever promising the rest of the band full member pay after the first few albums. I get where he was coming from as alot of people don't understand how much money it takes to run things, and alot of money was coming out of his pocket unlike say Ozzy who's father in law / label was footing most of his bills. And most of these sidemen weren't getting alot of pay back in the day, certainly not what we all thought they were getting.
Problem was he gave his word then reneged. Viv called him on it, the other guys didn't rock the boat because a little was better than nothing. Vinnie pretty much said as much recently. Even though by the third album the band was losing some steam, I saw that tour and it was still packed. I think had Viv stayed they could have gotten more years as a Gold Level selling act. All of Dio's follow up albums failed to go Gold after Sacred Heart. I don't think Dio was ever the cash cow Ozzy was but again, don't give your word you'll take care of people then don't.