Genuine question this: have you ever listened to much Beatles music? The variety of styles is something that defined them, they were able to move from pop songs like She Loves You to ballads like Yesterday and Here, There and Everywhere to proto-hard-rock like Helter Skelter to psychedelic classics like Penny Lane, Strawberry Fields, Lucy In The Sky, A Day In Thel Life and Tomorrow Never Knows through to Victorian kitsch on For The Benefit. Songs like She's Leaving Home and Eleanor Rugby sound nothing like anything anyone was doing. I pretty much could go on but they were able to do pretty much any style better than their peers as the link I posted showed. I forgot about songs like Within which is the first time Western artists had written an Indian piece of music.
As for just having 4 chords, you're plain wrong on that. They broke boundaries by basically taking influences from classical music, the tape looping of Avant Garde classical music, Indian music, folk music etc. They were superb musicians and have a listen to what composer Howard Goodall says about them - basically it's very complex music and they knew more about melody than a lot of classical composers. You simply cannot do this if all you know is 3 chords.
I totally understand how people might not like certain musicians - I don't like Bob Dylan particularly - but I am able to recognise his genius. I do think if you listened to Revolver, Abbey Road, Sgt Pepper and The White Album you should be able to recognise more than 3 chords and a complexity, as well as melody, that few have ever matched.
I do think that somehow it's become cool to dislike them and that's fine. However you simply cannot say they are overrated, wrote simple songs and knew little about music. It's like saying my mate Dave draws an apple better than Picasso so he is shite.