I agree, that Mozart, Bach and Beethoven all show extraordinary intellect and talent, which still challenges that of modern composers. But, it has to be remembered that at the time (without hindsight) the music these composers wrote was aimed at a specific audience, much like that of pop*. The audience was very much different, but it is this consistent ideology of audience engagement, which can be seen in any performer, and in any field of music.
The Beatles music or sound may not be classed as complex
but it certainly contains depth
. This is obvious and, naturally celebrated. Mccartney being a critical figure in the 'four-headed monster' can therefore be honored with such a comment.
Songs such as Yesterday, Penny Lane, Eleanor Rigby, Let it be .. etc
The above songs all show what you term genius
Oh, and the songs you have mentioned, its not like Lennon sat in a white room, cut off from all life, and wrote, played and recorded all by himself...howway, ever recorded yourself? It doesn't work like that. Mccartney input was critical to Lennon (and obviously vica-versa) so Mccartney can, like Lennon, be celebrated.
Mccartney as a seperate entity? Yes, of course!
The Beatles are the best at what they do, much like the classical comparison of Mozart, Bach and Beethoven.
* The term pop often troubles me. We all know the interpretation has changed over the decades, but using pop to front a negative view on the actual music is a modern misconception of meaning.