I'm on the fence here. In a way, yes, Sharon's actions weren't unprovoked. They were childish and unprofessional, and, I'd say, disproportionate, but she didn't act without pretext.
On the other hand, I remember having a very strong aversion to the idea of Maiden touring with Ozzfest at the time. I felt that This was the wrong venue for them, and that supporting another band, even if it was Black Sabbath, was degrading. I've always wondered if Bruce felt the same way, and that this is what triggered his rants. Earlier that year, Maiden had sold out major venues in Europe such as Ullevi and Parc de Princes, and headlined Rock am Ring, and now they were being forced into the Ozzfest corset. Maybe it was the right move business-wise, but maybe that's also what upset Bruce, that Maiden's status was determined by corporate considerations. I remember ranting all day when I lost my own office and got moved to a desk in the basement once, this sort of thing hurts.