Have you been close to these positions in a huge company?
I really don't think that's the case at all.
Ex: Look what happen to DIS after Iger left.
Most senior managers can coast for protracted periods as it's rare to replace the CEO in an upswing, and the CEO mainly has to not piss off those they work with. It's tough for any senior manager to read the tea leaves reliably, and as such - they are often replaced after N months/years when some decision goes poorly. The actions/results/impact of decisions are spread so far between that it's often difficult to assess a senior leaders impact in an organization.
DIS has had some high profile troubles since Iger left - but he may simply have seen the writing on the wall that the time to go out on a high note had come. I can think of several firms with similarly well-timed exits.
While the above scenarios reflect the CEO's contribution to an organization's ability to capture value - there is a useful debate on whether these organizations should be able to capture that value. If the organization has a monopoly, then they can arbitrarily increase the amount of value they extract at the cost of other, more productive, sectors of the economy. Over-rewarding organizations and their leaders for capturing value incentivizes such anti-competitive behavior.