Other groups had already done or were doing all that, Nick. The difference was that the Beatles could add excellent vocal harmonies and had a gift for the perfect commercial pop song. Let’s face it, Dylan’s songs usually sound better covered by someone else.
When you talk about fancy chords, to a guitarist they aren’t particularly fancy. The Hard Day’s Night sound comes form leaving a finger on third fret high e for most of the song. The major 7th stuff is really easy to play (I assume we’re talking about “I saw her standing there”) as you are moving pretty much the same postion around the fret board. And they were the chords and sounds of the time – Guitar Boogie by Chuck is another song in major 7th but takes months or years rather than days to learn to play.
Which brings me to another point. The orignal Jonhny B Goode is 170bpm, Jailhouse Rock is stupid fast. Rock and Roll had been fast frantic and a bit anti-social; the Beatles slowed it down, rounded the corners and made it easier on the ears to broaden the appeal.
And they had the press, radio and TV on their side. At four I was allowed to stay up late to watch the Beatles. There was so much hype that even my musically indifferent parents were dragged into it. The music was good enough, the look right, the voices great and marketing perfect.