Ringo missed part of a tour in 1964 due to illness and was replaced with a session drummer, Jimmy Nicol. It's true that some of the later Beatles recordings feature McCartney on drums, but by this time the band was fragmenting and it was not uncommon for a particular Beatle to record songs without much help from the others.
Of course, it was also standard practice for the rest of the band to swap instruments from time to time in the studio, often due to recording limitations of the day - Harrison playing bass when McCartney played piano, for example. The occasions when the drumming was handled by someone other than Ringo should not be seen as an indictment of his abilities.