If you want to know “What If?”, listen to the solo albums and that would have given you a pretty good idea.
Each had a great "solo" career that suggests to me that the Beatles would have probably continued as the top act in the world. Consider that you had four artists putting together albums. Had they still been the Beatles, they could have skimmed the cream off the top. Plus, the four combined seemed to have a synergy that is lacking in the individual works. Each of the songs would have been better as a Beatle song than it was as an individual song. A lot of that synergy is the George Martin effect IMO.
IDK about that...Lennon and McCartney always seemed to refine each others songs.