How is it "almost impossible to judge" for an outsider? We're talking about a business whose results are public, not your typical private corporation.
Just as in any corporation, where the results are abysmal, you're always going to hold accountable those who hold high positions in management, especially if they have been in place for a significant time. Begins with Bergevin, naturally, but then extends to his closest advisors and that includes Mellanby and given Lapointe's rising responsibilities, he should also be held accountable. You don't need to be a management consultant conducting weeks of investigations to be able to know that.
As to your second point, no one has said that if you hire individuals that you know and trust, they are automatically doomed to fail. All we're asking Bergevin to do is surround himself with the best in the business.
As for who Yzerman hired, it looks like he's done a better job than Bergevin. He's also owned Bergevin in a trade. So if he's hired cronies, I prefer Yzerman's cronies over Bergevin's cronies. And that's the bottom line -- give me the cronies that actually perform and I won't care if they are cronies. I submit that your average fan wouldn't care either.