In this PDF file of several chapters from the book The Beatles And Their Revolutionary Bass Player by bass player Dennis Alstrand,he explains that Paul’ McCartney’s bass playing was already first rate in 1961 only months after he learned to play it which he got stuck with because John and George didn’t want to play it, and he was not a bad bass player by 1963 and you can hear on The Beatles 1963 and 1964 recordings and live playing that he was already very good even on such primitive,limited sound systems with no feedback monitors so they couldn’t even hear themselves singing and playing yet they still sang and played great and in sync with each other and very limited,primitive recording technology recording technology and many people said this about his bass playing too in reviews of the remastered The Beatles Live At The Hollywood Bowl album and I could hear this too just from 3 minutes of samples on amazon.com.
Many people also said you can hear George Harrison’s great guitar playing,Ringo’s great underrated drumming,and John Lennon’s great underrated rhythm guitar playing, and Paul became a great bass player starting on The Beatles late 1965 Rubber Soul album.