I'm not military, so I'm talking out of my butt, here....
But it strikes me that in an organization like the Marines, a little turnover might not be a bad thing....
....Provided that it's not "politically motivated" and done properly.
I've no doubt about the latter. Marines always get things done right. The former, though, I'm not so sure about.
Two schools of thought on that. The US military has generally operated on a "move up, or move out" philosophy. IOW, those not showing potential to serve at the next highest grade (i.e. are "passed over" for promotion) get shown the door. In general it works well, but it does have its downside as well. Some officers will compete for command positions, not because they really want them, but because they need to "check the block," in regards to their career progression. Needless to say, in those cases, the soldiers under them are not necessearily as well led as they deserve to be. Another downside is that in many cases, an officer or NCO is placed in a position just long enough to display competence and really become proficient at their job, when they're moved out to give somebody else a chance. In some other militaries, you may have a company first sergeant or company commander in those positions for years and years (which also has its upside and downside as well).
It really is a double-edged sword...