... ... I have a theory about their songwriting and I've never read anything about this to prove or to disprove. Seeing how they played a variety of songs (rock, ballads, show tunes, etc.) I think John and Paul didn't just learn those songs but that they sat down and really studied those songs. You know, why do these chord progression work so well? Why does this melody work so well against these chords? I think they did a lot more homework than we could imagine. Of course they did their wood shedding and by their own admission wrote some very lousy songs when they first started. But they certainly paid their dues and once they got it right the world was theirs!
I agree with your theory. As budding songwriters, of course they would study the successful songs they liked and wanted to emulate. They often said this song, or that song, was an attempt to be like this artist, or that artist. Or they knew that the "call & response" was a powerful tool in a song, or that the falsetto parts got a big audience reaction, and so on. They admit to shamelessly stealing parts of songs from wherever they could.
My corollary theory is that they were also smart enough to take good musical advice. From Tony Sheridan, for one, about the big sound of dreadnought acoustic guitars. And later, when George Martin suggested they speed up the draggy "Please Please Me". I was shocked to read back in the '70s & '80s, that the records I loved were "take 65" or "take 93", or whatever! And these days, there's SO MANY alternate, preliminary versions of their tapes available that it's quite obvious that worked
extremely hard to get the right tempo, the right feel, the right "words" (or noises) before releasing a finished product. And almost no 2 of their recordings sound alike! As if each one is
the definitive take on that sound!?!
But, luckily for us, Paul doesn't mind playing lots of the oldies, starting with his MTV Unplugged show and even on up to his concerts today, with whatever instrumentation and setup he has available, warts and all. Showing us "the way"! While I do love a good Beatles tribute band trying to nail the exact tones and feels of the recordings, I also feel like any of us are free to play and sing their songs in our own voices, with our own instruments, our own feels, be they similar, or not. Heard a friend's band do a sped up version of Wings' "Bluebird", with a kinda syncopated middle part(!), a few years ago that really grew on me by the end of it. It's "the soundtrack of our lives"! Why shouldn't we make it truly ours?
My 2 cents.
.