Speaking of the non-Beatles songs they play in the studio rehearsals for the rooftop performance:
In his YouTube review of the movie, Rick Beato (whom I really like) marvels at how many songs The Beatles know (referring to the "oldies" they attempt to play). Well, they sort of remember those non-Beatle songs, but they certainly don’t perform them very well in those studio recordings. I know they were just "fooling around", but still. Their performances of those songs imo provide ample evidence that my assertion The Beatles were not a very good band---strictly in terms of being "a band"---is plainly obvious. You may disagree.
It was their songs that made them great, not their abilities as a band. IMO, of course. Most Rock bands are better at being a band than they are at songwriting. With The Beatles (no pun intended ;-) the opposite is true.