Sort of revisionist history on your part since we will never know. The Beatles songs were already covered by jazz musicians in 1964 on the strength of their chord progressions and melodies. Were songs by Chuck Berry and Buddy Holly being widely covered by other musicians who were not rock related? To say they would have ended like the Dave Clark Five is beyond being revisionist. I guess you have not heard what some of their peers were saying. Maybe the discovery of avant music and classical Indian music and being better musicains had something to do with their growth. I give George Martin credit for the classical influence on the Beatles.