Everyone has a role.  You need people to fill every job.  Not everyone gets to be the pitcher, play first base, be a designated hitter.  I ran into some people from a fairly "top heavy" team - that is, they have mostly senior super stars on their team.  I commented (without thinking) about how great it must be.  He quickly corrected me.

A team of all stars makes for a tough road for a lot of people.  Imagine, he said, if you manager was the best person at his job in the company.  He (or she) had done the job 14 times before, and consistently was recognized as a super star at that job.  What are your chances for advancement?  Obviously your manager is happy where they are, or they would have moved on.  Obviously they are good at their job, or they wouldn't have gotten all the accolades and repeat performances.

Healthy teams have a mix.  They have growth opportunities.  They have a reasonable amount of turn over.  A stagnant pond is a dead pond.