Paul McCartney is the Mozart of rock and he really was born this way because he inherited his father Jim McCartney's and Jim's father's natural music talent,to a rare ridiculous extreme degree. Paul's father Jim taught himself how to play the piano at age 14,and he broke an ear drum at the age of 10 so he was deaf in one ear,and he went on to become a classical jazz pianist and the leader of his own jazz band Jim Mac's Band who were popular in clubs in Liverpool. His father even wrote an instrumental song called,walking In The Park With Eloise which Paul recorded with the name The Country Hams in 1974 and included this song on their 1976 Wings album,Wings At The Speed Of Sound.
But his father and grandfather weren't poets,they were naturally musically talented and Paul has always been more of a *music genius* than a lyric genius even though he can and has written very good lyrics,but he doesn't have to.And even when he did it's his *music* that is what is so great about his songs and albums.
Paul's father's father,also played brass and other instruments in a band and was a good singer with a good singing voice so that must be where also got his once great singing voice for rock,love songs and everything in between.