"Can you pick the next guy that can do it? With 100% certainty?"
No, but I can't say with 100% certainty that Cook won't break something in the next year. Any person is capable of making a stupid mistake, many of which seem plausible at the time. The history of companies doing something disastrous for them is long, and many of them don't look like guaranteed bad ideas when proposed. 100% certainty is impossible, but you know that already.
There's a difference between being a visionary who can successfully take a company from nothing to a moderate success, or even from a successful company to a behemoth, and someone who can avoid crashing an already successful company. Steve Jobs had to be the former twice, getting the initial Apple products sold and rescuing the weakened Apple in the 1990s. Even that wasn't all down to him, but he played an important role. Cook did not have that problem; Apple was massive in 2011 when he took control of it, and it's massive now. You're right that someone could pull a Musk and break anything, even something as successful as Apple, but it takes effort to be that bad, as we're seeing with each bad decision that Musk makes.
This isn't to say that Cook doesn't deserve the money he gets. I don't particularly care about that. Apple's got a bunch of cash and decides to give it at any level they choose. Nevertheless, Cook's neither a miracle-maker nor the only person who can operate Apple.