In that analogy, what if those 10 books are Harry Potter + 3 others?
I'm not really sure what that means.
I could be the most mechanically proficient player in the world but complain constantly about x champion being OP or y system being broken without any real substantiated evidence to back it up. I'd probably be Diamond, but my opinion on game design is effectively meaningless. On the other side, I could have completely awful mechanics but have a deep understanding of the underlying mechanics of the game and be Bronze.
Stratifying based on rank is akin to saying that x champion is overpowered because they have a 53% win rate. Where is this champion played most? By whom? What sorts of matchups does the champion excel in? Where are the strengths of the champion centered and how is the counterplay designed?
Rank is not a valid metric for measuring the validity of someone's opinion. It takes into account an end result without assuming any other factors, which statistically speaking is completely and totally irrelevant.
I think you're kind of sidestepping the point. Let's go back to the book analogy, because I like it a lot:
I'm not going to pick my author based on the number of books they've read. I'm going to talk to their publishers, look at their writing samples, and conduct interviews. Similarly, I shouldn't be deciding the validity of someone's opinion based only on their rank. I'm not arguing that I should.
I am arguing that it is something of an indicator. If I've read 100 books, I may not know much about writing books, but I certainly know about books. By the same token, if I'm a diamond level adc, it's highly unlikely that I am clueless about marksman itemization. Is it possible that I am clueless, and I just make up for it with godlike mechanics? Of course. But it's not likely. Does that mean I know anything about how to change adc itemization? Not really. Butt I am probably qualified to talk about current itemization choices.