Just my 2 cents...
Unlike with "The art of fake guitar", I personally dont think of the Beach Boys or Beatles as virtuoso instrumentalists. So I'm not as concerned with who played what. For me, it's much more about the songwriting and voices.
First, I think it's obvious that the Beach Boys harmonies were very superior to the Beatles harmonies. Beach Boys' harmonies are so beautiful, in tune & steady that at times there down right heavenly.
As far as songwriting, I think the Beatles were more consistent & overall better lyricists. John & Paul were both genius writers. But Brian was like a mad genius. His music writing & harmonic concepts became more complex and explorative. He completely threw the rule book out.
Anyway, to quote Forrest Gump... "That's all I have to say about that" 😁