It doesn't help that NCO ranks have become a tool for military diversity hires. There was a time not that long ago when a Marine sergeant was capable of taking over a platoon if the officer and SNCO were killed. Now, a ton of E-4s and E-5s are malingering women or minorities with high PFT scores that have no practical fleet experience. I'd love to know the demographic statistics of meritorious promotion boards, but I'd be willing to bet it doesn't skew towards merit. If you're competing against a woman or minority for meritorious promotion, you might as well not even show up.
The military cares as much or more about optics than it does combat readiness, and having a ton of black/female leadership makes for great photo ops. Unfortunately that often doesn't translate to operational efficiency. I can count the competent female NCOs I've met on 1 finger, and she was practically a man anyways. I ended up under a command where the Sergeant Major was a black supremacist, and it became immediately apparent when a lot of experienced white guys were being replaced in their billet by totally inexperienced black guys and gals that had been fast tracked through the ranks. We had a young black E-3 that checked into our unit that ended up picking up sergeant within his first year in the fleet. That's practically impossible in the Marines. He never had the benefit of climbing the ranks naturally and was thrust into a position of leadership he wasn't close to being prepared for. Imagine your only experience is basic training and being put in charge of guys on their 2nd enlistment and 4th combat deployment. One day he walked into the SgtMaj's office, dropped a line of cocaine on his desk, and sniffed it up. The stress of being put into a situation he didn't have the experience to handle made him hit the wall, and he felt like his only option was to get out. We never saw him again, but had he stuck around he would have has an extremely successful career. They denied him the ability to learn the ropes and probably ruined his life over it, all because they wanted to create an image of diversity in leadership and had to abandon merit to achieve that.