Lots of people run things, and lots of them are really bad at it. I've known people who I would classify as way above average managers, and their success is not just due to having carte blanche access to internal state. It's due to being able to manage the goals and expectations and workflow of many groups of people, and being able to keep all of the different plates spinning. Ensuring that everything is moving in the right direction all the time in an organization bigger than a few people is not trivial, and if you think it is, perhaps you are not getting paid enough.
I also think if you can replace a given manager with anyone and the right information, then that manager is as worthless as you think they are. While that may be true of many managers, it's not at all true of good ones. I think there's the daily work of the business, and there's the managing of the daily work of the business, and while the skill-sets often overlap, they are not the same, especially as the business grows.
On the other hand, I find it hard to justify many (most?) of the highest end CEO salaries, but generally a competent manager at a company doing just several million dollars worth of business per year is worth at least several hundred thousand dollars per year (roughly how much someone who owns and runs a business with that much revenue would make).
At the end of the day, I'm going to have to take the cop out though and say that if you've never met a manager that can't be replaced by just anyone with the right information, you haven't met a good manager, because I definitely know at least a few people who can step into many roles, whether it's running a business, or coaching a youth sports team, or helping a local non-profit, where everything starts running better once they start providing direction and it's not because there was no one providing direction previously.