What about so-called experts? Ever notice how experts are often divided on subjects? Half the economists with PhDs say the economy is great, and the other half claim we're going into recession. Same with the stock market pickers, horse racing aficionados, etc.
Acutally, all economists agree whether the economy is good or bad. It's how to fix it when it's bad that they don't agree upon, which is normal because so much of the (of our) economy is based on speculation. As for horse-racing experts, well, pretty normal they can't agree on which horse is gonna win, no?
Elsewhere, if you take the time to look, you'd realize that 99% of all scientists agree on 99% of scientific matters, from the creating of the universe to the effects of man-made climate change. Those who disagree, or spread misinformation about such matters, are either non experts but pretend to be when they have a camera in their face—and I'll stop here because this can get political very fast.
It's worse in the arts where so much is feeling, emotion, innate talent, etc. How do you measure these things?
Now if you are telling me that art critics and art historians don't agree that Da Vinci, Delacroix, Monet, Caravaggio, Velasquez, etc., were all great painters, that Cartier-Bresson, Robert Frank, Dorothea Lange, Diane Arbus, Robert Adams, Gordon Parks, etc. were all great photographers, and that the greatness and depth of their works, way above what the average artist or photographer can do in a lifetime, cannot be described, then we really have nothing to talk about.
I don't know why you make this about fame. We're not talking the Kardashians, who are famous because they are famous—that very modern phenomenon in which fame is both a means to an end and the end itself. Cartier-Bresson, Robert Frank, Dorothea Lange, Diane Arbus, etc., are famous because they produced great work. And people talk about the greatness of these works not because the people who produced them are famous but because they took the time to look at the works, think about the works, be moved by they works and try to understand what makes them great, including all that is inherently mysterious about the greatness of works of art.
Are there non famous people who have also produced great works? Of course! Just think if Vivian Maier's work would not have been found and simply destroyed after her death. That in no way diminishes the greatness of the other artists' accomplishments.
Now if you don't believe in greatness, if you don't want to acknowledge that of Cartier-Bresson's work, or if you don't want to stop and take the time to try to understand why so many people see greatness in his works, that's your prerogative. To me, it comes to a question of trust, of levels of trust. When Ernst Gombrich tells me about the greatness of an artwork, I trust him, not because he bears the title "expert", but because I've read him, tried to understand what he says about art—
The Story of Art is a fantastic book, by the way—and decide that he's an expert I can trust. That's how it works.
Now if you don't trust anybody's expertise, if you don't trust the fact that some people have more knowledge than you and that you can learn something from this knowledge and better understand the works of art you love and admire, to me, that's entering a realm of pure cynicism in which I cannot find myself. And it goes against my deep belief that ignorance is a blessing and the ability to learn from others a blessing.
He'd admit that Joe Dude-Guy on YouTube can have a level of fame but questions how serious he is. But if Joe Dude-Guy wants views on YouTube, he has to provide his audience what they want.
I'd say the same thing about Joe Dude-Guy than stated above: levels of trust, and audience expectation—because, as opposed to all great photographer, he's playing for an audience, as you adequately point out.
I'm not dismissing Joe Dude-Guy, to make it clear. The ones I've found I can trust have guided me immensely, from helping me buy my Pentax 67 to figuring out how to bleach my prints (honestly, a life-changer).