I’d imagine if they had done another album or two, they would have contained a lot of the songs they ended up doing solo afterwards for the next few years, with or without some tweaks. Some of their later albums were less collaborative anyway. You could start telling the difference between a Lennon and McCartney song by the last few albums. And then you had songs like Day in the Life which just became a medley of the Lennon and McCartney parts, because their styles had grown so different.
John was a product of the 60s, where Macca’s stuff is more timeless.