I know enough to know that there is NO ONE who is indispensable. There are thousands of qualified E-6s who are passed over each year because of limited E-7 slots.
My 34-year-old son told me this past weekend that one of his high-school buddies just made chief so I’m glad for him that a slot was there. OTOH, there is no way that every one of these 8000 is marginal or non-performing. The USN will sorely miss some of them.