Maybe not in your opinion, or my opinion, are the Beatles the greatest band, and the greatest musical ARTIST, of all time, but they are very much that statistically.
The Beatles song Yesterday has been covered by over 2,200 artists, more than any other copyrighted song in history.
Even individually the Beatles dominate.
Their bass player, John Lennon, for example, sold 14 million albums in the US and was responsible for 25 number-one singles on the US Hot 100 chart (either ones he wrote and sung himself or he wrote for someone else). In 2002, a BBC poll on the 100 Greatest Britons voted him eighth and, in 2008, Rolling Stone ranked him the fifth-greatest singer of all time.
McCartney has written, or co-written 32 songs that have reached number one on the Billboard Hot 100, and as of 2014 he has sold more than 15.5 million RIAA-certified units in the United States.