We (tech people) are replaceable, just that replacing us takes a lot of time, effort and money.
I know it feels like nitpicking, but I never felt that any of the developers were actually hard to replace: it takes some money, time spent on recruiting, interviewing, then training, but in the end, the new people catch up in a matter of months and the resources needed to invest in a replacement can be relatively easily estimated.
I usually don't see that with very good business and product people. When they left the company, the team became demotivated, the lack of company and product vision caused frustration, the company couldn't find a replacement at all, caused turnover. In my experience, good business people leaving is the early sign of the company going south.
The causation can go in both directions, though: 1. product and business people are the first to see if a product/business model isn't working out, so they leave. 2 they leave, then they can't be replaced, replacement is only half as good, people quit because of lack of vision, things go even worse, more people quit, company has to shut down.
Senior leadership is the hardest to replace. Marketing managers or sales agents or the director of HR or a jr accountant or product managers are easy to replace and change happens often. Changing the CEO can be a big transition but replacing the product owner on the main app shouldn't be too difficult and happens often enough.
In your example if the product manager sees the plan is not working out so they leave. Is it their business model? If so they are running away from a mess they created. If the model comes from above than senior leadership is lacking.
Not being able to replace would point to a problem with either HR or senior leadership .
I'm sure there are senior leaders who are amazing, and would be extremely difficult to replace. My experience of "senior leadership", however, has been, almost universally, that they're in that position because they were born into money, their organizational skills are crap, and they think "vision" means "sticking with the status quo (with maybe one oddball quirk) and "leadership" means "yelling at people until they do what you want."
That kind of "senior leadership" isn't hard to replace at all.
I see where you're coming from, but consider the cost of the replacement process itself: it can be chaotic jumping from one set of crap organizational skills to another. Point being, it's not so much that the person is very valuable themselves, but more that higher position = bigger disruption.
In fact there might be a slightly counterintuitive relation here: assuming good intent on all sides, transition from a leader with good organizational skills would be less disruptive.
You're not wrong, and I think that your last point is actually very true—and that this is part of what lets the leaders with crap organizational skills get away with it. It's not immediately obvious that their terrible leadership is ruining the organization.
What's needed, IMO, is a cultural shift away from the idea that we need a singular, extremely powerful CEO/president/chairman, and toward more group-oriented decision-making processes and devolution of both responsibility and power.
We abandoned absolute monarchies for a lot of very good reasons, and one of them is that having one guy who can just walk into any room in the kingdom/company and exercise the power of (in this case, financial, but that often becomes very literal) life and death over anyone else in there is a bad thing.
A lot of the ability for senior leadership to get things done is due to the network they've built inside the company, and their understanding of the power dynamics within that company. This is less and less true the lower you go in the ranks. Therefore it might cost some extra money to replace that IC, but nothing like the hit to productivity that switching senior management could cause. One way to guard against that would be to adopt a model where senior management are routinely switched so that the working level becomes robust against changes in management.
I know it feels like nitpicking, but I never felt that any of the developers were actually hard to replace: it takes some money, time spent on recruiting, interviewing, then training, but in the end, the new people catch up in a matter of months and the resources needed to invest in a replacement can be relatively easily estimated.
I usually don't see that with very good business and product people. When they left the company, the team became demotivated, the lack of company and product vision caused frustration, the company couldn't find a replacement at all, caused turnover. In my experience, good business people leaving is the early sign of the company going south.
The causation can go in both directions, though: 1. product and business people are the first to see if a product/business model isn't working out, so they leave. 2 they leave, then they can't be replaced, replacement is only half as good, people quit because of lack of vision, things go even worse, more people quit, company has to shut down.