Paul once described the Beatles as, "a good little rock and roll band."
He should know. Still more people could tell you about the Beatles and their songs then they could about Quincy Jones.
Yep, even Paul knew they were a sum of their parts (and their songs) more than a group of trained virtuosos.
I always found each Beatle a bit unconventional in their approaches to their instruments. But that's rock and roll, and it created a unique sound that suddenly half the bands around the world wanted to imitate.
One thing that is hard to take away from The Beatles, even in a technical sense, is their approach to vocals, the quality of their lead vocals and especially the chorale harmonies they produced, largely with three voices. Very clever vocals, high quality stuff by any standard.