Don’t forget that other organizations can grant rank to a founder of an organization if that person is willing to accept it.
Shigeru Oyama (no relation to Mas Oyama) left Kyokushin in the early-mid 80s and started his own organization - World Oyama Karate. A few years ago one of the major Kyokushin branches (quite possibly IKO 1) promoted him to 10th dan, recognizing his contribution to karate as a whole, and a lifetime achievement award in a sense. I think he was deserving of it; along with Tadashi Nakamura he brought Kyokushin to North America and turned it into the major force it is/was here and internationally. He started and grew a highly respected international organization consisting of many highly regarded students and instructors. He was truly a legend in knockdown karate. The promotion came no more than a year or two before he passed away.
Tadashi Nakamura did not promote himself to his current 9th dan. He was promoted to 7th dan by Mas Oyama during his Kyokushin days in large part for his massive contribution to spreading Kyokushin internationally. He served as the chief instructor at the Kyokushin honbu in Tokyo for quite some time and was considered by many to be the best teacher in Kyokushin. Many years after leaving Kyokushin, he was promoted to 8th and 9th dan by a budo organization in Japan. I’m not sure which one, and I know he didn’t ask for it. He doesn’t advertise any of this, other than briefly mentioning 9th dan in appropriate places. He’s reportedly stated a few times that he would never accept a 10th dan because he’s still learning.
There’s plenty more people out there who fall along these lines. Not every high ranking yudansha promoted him/herself in an attempt to pad their resume, gain unearned respect, sign up more students, etc. They’re certainly out there, but they’re easy to spot if you’ve got a little understanding of how ranks work and what they mean beyond one or two organizations.
When you look at it that way, I really struggle to figure out how a guy who runs a dojo in a strip mall and only has a handful of students who’ve successfully run their own dojo or doesn’t have any who’ve done so has “earned” a high ranking rank. Unless of course they’ve “been there, done that” in a highly respected organization and recently broke away.
As far as people promoting someone above their own rank goes, I think some people overthink this one. Is it really THAT HARD for a group of worthy high dan ranks to say “this guy is at another level.” If basketball had dan ranks, I don’t think it would be too difficult for a group of some of the most respected players to say “these guys are far better and greater than us.” Radical concept here, huh?
IMO the highest dan ranks should be the people who’ve made the biggest impact on the art. The ones who’ve spread the art on a large scale, and/or the ones who those guys go to for their training. Take a guy like Meitoku Yagi. He was given Chojun Miyagi’s belt and gi by Miyagi’s family. As far as I know, he didn’t bring Goju Ryu to the masses on the level that someone like Gōgen Yamaguchi did. But guess who Yamaguchi and many of his peers went to to get further training? Yagi. They considered him the encyclopedia of Goju kata in a sense. Do you think Yamaguchi and his peers couldn’t nor shouldn’t have the authority to promote him to a rank higher than their own? Even stupider question - do you think Yagi cared much more than a simple “thank you very much” if they promoted him? I doubt a guy like that needed that sort of validation.