No.
You are drawing the wrong conclusions.
From a personal stand point a promotion is good. It's always good for coaches to better themselves. When they do, that is success. They are doing well, and people around them must be benefiting from them doing well. We celebrate people being successful. It's the American dream coming true.
For a staff, sure it would be great if you had all the best coaches and they never wanted to move on to better jobs, but that's not how it works. You have success, and some will leave to get better jobs whether bigger schools, more money, or more responsibility.
The idea that you celebrate success of a coach and therefore, magically your staff isn't going to have to replace that person is illogical. Ideally you have a fine balance of both. Coaches moving on to better jobs due to success, and another round of coaching who joined your staff via a promotion from within (or outside hire) who then bring new ideas and further success.
Is it always a straight line to success? 50 years of Gophers football would tell us the answer is "no".