Bad analogy. Oprah doesn't write. Though she influences their bank accounts, Oprah doesn't influence the creative output of the people who create literature, not to be confused with the publishing industry.
Particularly regarding the Beatles, most people who rate them highly do so on the strength of their impact, not the merit of their individual songs. After all, they had their own influences. They may not have been that great musically, but they were great in their influence on those who came afterward.
It's not a perfect analogy because the Beatles didn't invent rock 'n roll, but to say they were overrated is almost like saying Edison was overrated because his light bulb had an ugly color of light, it was noisy and it didn't last very long. It's kind of missing the point.