If you read Espo's book he makes it sound like Bergeron continually harassed him to make trades for aging French players (many of which he refused to do), anonymously leaked details of proposed trades to the media that nobody else knew about, deliberately sat out players Espo wished to trade in order to sabotage their trade value, etc. It's clear Espo had no use for Bergeron but he said the reason he fired him was because he couldn't be trusted to shut his mouth about the details of Phil's various proposed trades, or other about private conversations with Espo, which Espo considered to be a Brutus-like betrayal. He describes how he fired Bergeron and his glee in doing so in that part of the book.
I am pretty sure Espo at that time privately told every GM in hockey what he stated very publicly in that book, which is that Bergeron was a backstabbing, betraying, insubordinate, anti-Anglophone blabbermouth, and these character questions had as much to do with Bergeron not getting hired again as concerns about his health. GMs in hockey have no use or patience for such nonsense.
There is no doubt Espo had a huge ego and a ton of pride that was easily hurt, and he quickly wore out his welcome in management of several hockey teams. However, those "flaws" are somewhat apparent in the way he writes about his life in his book. You don't get the sense that he is a liar, however. I think from his perspective this is how things went down. He probably saw Bergeron as a yes man who would bow to his authority, and was genuinely stunned to find out he wasn't.