Firstly, Brack was only president for 2 years and a lot of these incidents happened prior BUT if you're in charge you're responsible. That's part of the deal that comes with that giant pay check. You don't get to say "it's not my fault". So Brack absolutely should go because he's seemingly failed to correct the toxic culture.
You'll note the email talks about "Blizzard", not "Activision Blizzard". This is how you can tell Kotick is distancing himself from this. It's "Activision Blizzard" when things are going well and "Blizzard" when it's not. Kotick is I'm sure busy selling this narrative that Blizzard is an autonomous unit. It's not. It's fully Activision at this point.
Activision Blizzard has squandered their most valuable properties. The only thing propping up WoW is a 15 year old version of the game that's quickly being ruined with the exact micro-transactions that ruined the game to begin with. Does anyone still care about Overwatch? Prediction: Diablo 4 is going to disappoint. This is the same company that brought you Diablo 3 after all.
As for the new co-leaders, ugh... this just screams PR. One of them is a woman of course. I'm not saying she's unqualified (although both of them are relatively recent hires, interestingly). But you know given the lawsuit that this was going to happen. But the main issue is that there's two leaders. We all know countries need two presidents, armies need two commanders, etc.
So what this suggests is that Ibarra had the confidence of Kotick and the board, she would now be president. So she's co-president because of the lawsuit. It may not be true but that's how people are going to interpret it.
To get out this rot it can't stop at changing the executives. Blizzard honestly needs someone to come in and clean house. This goes beyond the lawsuit, which is no doubt a relatively small minority. This is about half the company probably being useless.