To me, to ask this question, is like asking, what would The Beatles have sounded like if Ringo had played lead guitar, or if Carole King had written all their tunes. McCartney and Harrison didn't become a songwriting team, because Lennon and McCartney were the strongest and most prolific writers. There wouldn't be a Beatles if Lennon and McCartney weren't the songwriters they were. Harrison wrote a few gems of course, especially later on. But it wasn't like George had a store of great tunes that were ignored by Lennon and McCartney. When he came along with one that was really good, The Beatles recorded it. This is in no ways a slight toward George Harrison, whose lead guitar, vocals, and occasional compositions, were a key ingredient in what made The Beatles, The Beatles.