This is true if you are running a car wash. Even the mid tier employees satisfactorily do the job and customers can be given what they paid for. You are competing on geographic location and ability to do a very easy task repeatedly over and over. You get another chance to sell your product every single day, and you can adjust your prices up and down to find the sweet spot because the sales cycle repeats every day.

It is not true if you are determining the correct feature to add to microsoft's money making products. That requires deep knowledge of users and the industry and the existing product. It requires understanding the industry and users far in advance, the turnaround time for a feature in Windows or Azure is likely 6 months or longer, sometimes years. It requires acumen and an ability to think about customers and the market and sales. Microsoft doesn't have 5000 people who can do this. They probably don't have 1000. These people can go start their own business or consulting firm today. There are lots of people they worked with in the past who know how good they are so they can get another job.

The same is true for engineering. Out of 500 engineers, there are 10-20 that are doing the really important work that you can't just find someone else to do. They know everything about the system and everyone comes to them for advice or to get explanations about how things are put together and why. You can't just find some average engineer and put them in the same desk as these 10-20 and magically things are fine, the mid tier person doesn't have the years of experience nor the potential to fill this role even if they did have the experience.