If your organization has a ranking system and you're within that organization you'll understand how "valid" the ranking is, how useful it is (or isn't), etc. after you've been there long enough. The irony is that most who get into the higher ranks begin to realize that ultimately it isn't about rank -- most are just there because it is what they do and they like doing it. So you keep doing it. And then one day you get asked to test. Or you get far enough where you can't test anymore and someone hands you the next one. You say thank you and life goes on. The value will depend on the group, where you are and what you're looking for.
I remember having the realization hit me partway through my sandan test that this was going to be my last formal test (we only test up to sandan in Seidokan). "Hmmm, how did I ever get to this point? Where did the years go? Oh, well, no matter. I'm having fun..."
If you're in an organization that doesn't award rank, great as well.
If you try to compare ranks across organizations, well, best of luck to you.
If you're trying to compare testing methods across groups, ha!, well, enjoy yourself. That's kinda like comparing apples and zambonies...
Frankly those without rank who complain that ranking is meaningless often sound about the same to me as those with bloated and often made-up high ranks who boast about how great it is. Two sides of the same close to worthless coin. I can't count how many guys have shown up in the dojo over the years who have read all the books and then tell us how many different martial arts styles they've studied. Gone from one to the other. Or the dojo-hoppers. Those who never stay long enough to really get all that good at anything. Usually under 30 year old guys who claim "proficiency" in 5 different arts already. I'm in my mid 40's working on feeling passable in one. Maybe I'm slow. Anyway, these guys usually have an overabundance of confidence with a complete lack of ability to compensate for it.
And after a few weeks (rarely months) they wander out never to return again adding yet another style to their "resume" before they go and start up their own dojo with their own "eclectic" style of whatever it is they're doing. A gigantic, wide pool that's exactly 1 mm deep that will not be able sustain life... A little of everything but no depth whatsoever.
Anyone who trains any amount of time knows full well that ability is not reserved for the high ranks. Nor is intelligence, humility, or anything else. But rank within many groups does mean someone has been around a while, has trained hard, has passed tests, and has as a result demonstrated ability on different occasions. Those without rank may have done as much work, but just without the tests. And there are those without rank who have never demonstrated anything other than the ability to type on internet forums and hop from one dojo to the next.
But rank within some organizations means precisely what it does within that group. And for many groups it is a sign of progress, ability and contribution. And that and $5 will get you a cup of coffee at Starbuck's (no, wait, sorry, that would be a venti mocha blah blah blah blah).
Frankly I just look upon it as time on the path. Some move faster, some move slower, but progress is something else entirely. And ultimately we're all on the same path, some have just been there longer. Ideally rank helps us understand some of that within the context of your own organization. No guarantees, no absolutes. It is silly to take it too seriously. It is equally silly to just toss it out as worthless.
Much ado about nothing.
If an organization doesn't have rank, so be it. However, even the koryu organizations have structures. It might be simply kohai/sempai style, but they also have various things like menkyo, etc. The rankings may not always be overt, public and formalized, but they're always there.
So just train and figure out what it is where you are. And then train more because nothing really changes.
More mat, less chat...
Frankly, however, sticking with my Shakespearean theme, I do think some doth protest too much sometimes...