This is getting scary Nimrod. For a long time I disagreed with a lot of what you said, now I am agreeing with most everything you say.
I agree that you have to have studied something scholarly to even begin to say it is overrated.
As the original topic was The Beatles being overrated, if someone says that, it is nothing more than an opinion backed by...nothing. There is substantial evidence that The Beatles are at least one of the greatest Rock N Roll bands ever.
I have no problem with someone saying, "I don't like the Beatles". Okay, there are many bands I don't like. Rush is such a band, and yet I would never call them "overrated". I am not an expert on Rush. I think Neil Peart is a very good drummer. Not among my list of favorites. He is considered, by some, as one of the best Rock N Roll drummers. If I was so egotistical to think my opinion was so great, I would say he is overrated. I don't think that is my place to say that. He is just not among my list of drummers, I like. I don't like Rush's music and don't want to hear them.
I think it is a lack of respect for others opinion to say something is overrated without the scholarly education and knowledge to do so. If you insist on saying something have the backing and evidence for what you say. Making a blanket statement without presenting your case is ignorance.