That's only partly right. Stuart Sutcliffe (the band's original bassist), George Martin (the band's producer / arranger / sometime piano player) and a few other studio players could all be considered members.
My personal favorite is McCartney, in part because I am a bass player myself. Both Paul and Ringo had this knack for playing exactly what was needed -- nothing more and nothing less. Listen again to "Something". Although it was George who wrote, sang and played lead guitar, it's Paul's bass part that really makes that song amazing.