Their best songs were written by John all by himself. Or he would bring in a mostly complete song to a session,
and they finished it off together. Something like "And Your Bird Can Sing" is mostly John. From 1963 thru 1965
John was prolific. Paul wrote simple tunes that only sometimes reached greatness, like "And I Love Her".
The, "I added a word or two" stuff doesn't mean much to me. Paul wrote "Hey Jude" and "Paperback Writer" by
himself in my book. Paul wrote plenty of songs mostly by himself once he got good at it in 1965. He became
prolific in 1965, and stayed in the groove until about 2000.
By 1966 they were not writing much together. One of my very favorites after 1966 that they did write together
by putting two pieces together, as they did with "A Day in the Life", was "Baby, You're A Rich Man".
The effects of drugs on John is a sad tale. He wrote some really great songs in India, but after that his writing
leveled off. John became more a fan of sleeping and doing drugs from 1968 on, and for the rest of his life he
only wrote about a dozen or so songs that I would say are in the "really great" box.