There was a department store owner that famously said "Half of my advertising dollars are wasted. The problem is that I can't figure which half."
The same is true of middle managers. There are some that look as if they aren't doing much, putting in only 9-5 work. But they have key experience in how thing work, and how things are run. Others are involved in every decision, but it's really that they are constantly making sure that everyone thinks that they are important.
If you get rid of those with deep experience, the company might never realize what they have lost. Or why they end up with systems that grow complex patches instead of simple fixes and improvements.