Over how many years is irrelevant really it’s the volume that makes the legacy. In a hundred years no one will care if a song was made in 65 or 95.
Lennon and McCartney however pissed on everyone else and not by a little either. The chasm is unrepeatable. You could argue about the lot way below them all day though.
I agree - the quality, quantity and variety of their song-writing marks them out as one of the greatest composers of the 20th Century. Whilst other bands like The Rolling Stones and Beach Boys were absolutely brilliant, they just don't come close. Imagine being able to write She Loves You, Please Please Me and All My Loving as great pop songs, then doing acoustic numbers like Yesterday, She's Leaving Home and Eleanor Rigby, psychedelic classics like Tomorrow Never Knows, Strawberry Fields, Lucy In The Sky and A Day In the Life, love songs like Here, There & Everywhere, Long And Winding Road and And I Love her, album tracks like Because, The Abbey Road medley, Got To Get You Into My Life as well as great pop songs like Hey Jude, Let It Be and Get Back. Imagine releasing a double-a-side of Strawberry Fields and Penny Lane because you could! Just astonishing. Leaving aside the quality of the songs, the variety amazes me in itself, who else comes close to being able to do it?
Obviously, I'm a big Beatles fan, but when you look at their albums, it's amazing how many albums songs are widely known. I honestly don't think we will ever see their like for a long time. Not only that, but the speed they were writing albums and how quickly they moved on is still astonishing 60 years later.
After the Beatles, both Lennon and McCartney did some great songs. The problem they had is that they will always be judged against the songs they did with The Beatles.
Lennon did some great songs in the 70s - Instant Karma, Love, War is Over, Woman, Give Peace a Chance, Working Class Hero, Jealous Guy, Watching The Wheels etc. All brilliant songs. McCartney did too with Band On The Run, Suffragette, Live and Let Die, Coming Out, Another Day, Silly Love Songs, My Love etc. Again, anyone else in the 70s would love to have written these songs.
As The Beatles, they were - and will remain - the greatest composers of popular music for the foreseeable future.