I think the response from McCartney probably solidified that image:
Interviewer: Is Ringo the best drummer in the world?
Paul: He's not even the best drummer in the Beatles!
I'll be back.
You can't take anything that megalomaniacal jerk says seriously. Paul thinks he was the only Beatle that really mattered.
Lennon said it, not McCartney.
All the better then 
Yes, but Lennon also said that Ringo may not be a good drummer but he was a very good Beatle. In other words, his persona was a better fit for the image they were going for in their marketing of the group at the beginning.
Remember Lennon and McCartney both thought the band would last a year or two maybe and then they'd parlay that into a songwriting career.
They weren't thinking about the band becoming a musical force.