Paul was definitely the best musician in the group. I don't think that there is any musical instrument he hasn't mastered.
I remember years ago reading an interview with George Harrison, and as they listed to various Beatles songs, the interviewer would say "Love your guitar on that song George!" George would reply: "That was Paul."
Yep, on the song “Maybe I’m Amazed” every sound on that song, came from Paul, guitar, piano, drums, bass....all him.