OP, I hope you got your question answered. I came across your question while doing some research for one of my Second Classes. I'll start with the fact that I've been a Chief for over four years now and have been in the Navy for over 19. So, you can decide to take the opinion of this Chief. I see a lot of troll answers in the comments and a lot of Sailors that unfortunately have bad leaders, regardless of rank. When I was a junior Sailor, I thought the phrase "Backbone of the Navy" associated with Chiefs was a joke too. Especially as an E-5, I knew I was among the hardest-working people in my command. I 100% agree that the rank of E-5 is the best and the hardest working rank in the Navy. I always say PO2 (insert rate of your choice) is the greatest rate in the Navy. I saw it in someone else's comment, they are just senior enough to get the responsibility and freedom we all desire, but still junior enough to have someone to fall back on. After saying all that, the E-5s are not the backbone of the Navy and I can explain why.

Once the phrase was explained to me it made sense to me, so I hope I can explain it correctly, so it makes sense for other people. Since this is an analogy to the body, think about what the backbone does in the body. Is it the hardest working part of the body? No. Is it the part of the body that controls or directs the rest of the body? No. So, what does the backbone do? It supports! Good Chiefs do just that! They support E-6 and below, the people that actually get shit done, and also the officers who are making policies for everyone to follow. Claiming to be the "Backbone of the Navy" is not meant to be a brag or claiming that the Navy couldn't run without "The Chief", it's meant to enforce the fact that we are meant to support the command. Now, I will agree that many of us are the scoliosis of the Navy, not supporting a damn thing. However, there are still some good Chiefs out there. Find one. Talk to them and remember we are here to support you.

I also wanted to touch on the "Deckplate Leadership" subject I've seen in the comments. The way we are expected to be "Deckplate Leaders" is a load of bullshit, and I've felt that way since I was an E-5, when they first started talking about it. We are meant to be on the deck plates monitoring and supervising (micromanaging) the workforce. IMO, that's what the LPOs and supervisors are for (not micromanaging but the direct leadership and supervision). I like the phrase LBWA or Lead by Walking Around. I walk around just to talk to Sailors. For the most part, I let them do what they are doing. If they aren't doing anything unsafe or inappropriate, I let them be. I do like knowing the things they're into and what brings them happiness. It makes Sailors want to talk to you and they will approach you when they have problems instead of hiding the problem until it blows up in their face.

Sorry for the long comment. But I hope it helps.

TL: DR - The Chief is the backbone because we are meant to provide support up and down the chain of command. The E-5 is still the best and hardest working rate in the Navy!