There's a subtle but very important difference between making sure nobody is a "single point of failure" or bottleneck (heck, most great engineers will actively work with management to make sure they're not single points of failure!), and recognizing that engineers are not fungible resources and should not be treated as such.

I do agree that it's simpler for management to pretend that they are, and that's why great management is insanely rare. But great management, like great engineers, can make a huge difference in the success of a company / project.