I mean, isn’t that always the case though? That lots of people don’t belong there? It’s just the law of large numbers + the ever shifting lives of people.
Don't see why this should always be the case. Also I don't recognize your use of addition and the sense in which you invoke the law of large numbers.
There is no hiring process that is perfect. Plus, people burn out, organizations shift focus, etc. People who shouldn’t have been hired in the first place make it in, and people whose skills no longer match the job hang on.