Abba made many fine schlagers, Benny & Björn surely knew how to forge a hit, I hum to a few of them every now and then. But did they change the way pop music would develop? No. Even their own progress was pretty limited: the evolution in their tunes happened in the sound, along the general progress of dance and disco music.
The Beatles, on the contrary, left an everlasting mark in pop music, and within six or seven years made an incredible progress from making simple love songs into an artistically and politically strong figurehead. Revolution 9 could have come out from the WDR studio of experimental electronic music, and IRCAM had not even been established yet.

Luckily it’s possible to enjoy both Abba and The Beatles. 🙂