I appreciate your question.
First off, the US military today is better-trained - and *much* better-paid (and with a wealth of benefits) - than ever before.
Sure, that sounds like BS advertising...but it's true. Where else can you retire after 20 years on a livable salary, with relatively generous disability benefits, and have full health coverage for you, your spouse, and any dependents 26 or under? Oh, and your health insurance is accepted (for 'only' 75% of costs) in over 100 nations (and by over 100 health care facilities in Manila alone).
I know, that's not answering your question. I just want you to understand the military is not just some mindless grinder of hearts, souls, and bodies.
When it comes to rank, the best answer is, "it's complicated." Sure, the officers-and-enlisted thing makes it seem purely two-tiered, but it's anything but. For enlisted, there's E-1 to E-9. E-4 and above are considered non-commissioned officers ("petty officer" in the Navy). What that means in the real world is that unlike Russia and many militaries of the past, those enlisted with sufficient rank, experience, and training garner real authority. For instance, I mainly worked in Engineering on both conventional and nuclear ships. Imagine six enlisted men, all E-5 and below and no more than an official high school education, running a nuclear power plant. That's fairly normal. Mind you, they're supervised by senior enlisted and officers in another compartment, but those six young men are operating a nuclear power plant - they know how to bring it online, how to maintain it, and how to shut it down. I tried to qualify to be a "nuc" , and found out the hard way that a rural Mississippi education does not prepare one for Nuclear Power School.
I'm trying not to get off track here, but once one advances to the senior enlisted level - usually E-7 and above - one of the more important duties is to train junior officers. In the Navy, that's one job of the chiefs: to unf**k the minds of junior officers who think they're better than everyone else. They have a very real impact on whether those officers can continue on with a career. Sure, senior officers are famously prideful, but in the US military, every single one has received a dose of humility courtesy of senior enlisted members.
We're not done yet - there's officers, and then there's officers. The officers on track to take command of units are line officers - a *very* competitive bunch, as you might imagine. But there's almost as many *staff* officers who are not competing for command, but stay in their respective professions (supply, engineering, etc.) and become subject matter experts. Then there's warrant officers and limited duty officers, both of whom are comprised of former enlisted.
Which brings me to the next point: the enlisted are not necessarily restricted to only enlisted ranks. Those who get a degree (which is much easier now, btw) and who show exceptional professionalism are encouraged to try to become officers. Any retired military like myself will have seen this on several occasions...like the one who saved my life on my last day at sea (long story).
Lest you think the military has it easy, let me assure you that compared to the degree of responsibility most of us hold, we're significantly underpaid compared to the civilian world...but the benefits certainly make up for it.
In my opinion, the most underpaid person on the planet is the captain of an American aircraft carrier. They make, what, maybe 11K/month, with probably a bit of proficiency pay included. That might sound like a lot to some, but consider this: he's directly responsible for @ 5000 men and women (on *and* off duty, mind you), an entire airfield with 85-90 aircraft flying at all hours and in almost all weather conditions, foreign diplomacy, intelligence gathering/processing/interpretation, and oh, also those two nuclear reactors, too.
Try to find a civilian who would do all that for even ten times as much money. Our captains are incredibly underpaid...but they love what they do (though it can sometimes be heartbreaking).
Here's something else to think about: a carrier's flight deck is said to be one of the most dangerous workplaces in the world, and rightfully so. *But* accidents are relatively rare. Why? Because of constant training and discipline. My last deployment was on a carrier - about 5000 men and women - and we ALL came home safe (along with my injury, of course). Now go look at any community in America where there's 5000 men and women, aged 18-45, and see how many deaths there are during a six-month period. Outside of combat, service in today's military is in many ways *safer* than civilian life. Again, training and discipline.
Lastly, I retired as an MM1, an E-6. The lesson here is that even as a mid-level enlisted man, I understood and appreciated the above. Sure, we're all human with warts and all, but for the most part, the enlisted and the officers understand, appreciate, support, and even *sympathize* with each others' levels of responsibility.
So...no, we don't need a RAND study to determine whether our system works - it does, very well indeed.
Addendum: I'm a writer. Ask me a question, you get a freaking dissertation for a response. Sue me.
:)