I am with you on the first two, not so sure on the other two... Could you explain why you think this way?
In 1966, people were pretty used to the Beatles and the British invasion in general. Let me back up, the basic principle is seeing something for the first time, getting used to it, then seeing something coming out of left field that just knocks your socks off!
After Bill Hailey started the genre with Rock around the Clock, a lot of bubble gum copy bands sprouted up, then Elvis comes along, a white guy singing black blues. I won't even get into the stuff going on below his waist. But after this, Elvis went into the army and the groups that followed (with the exception of the Beach Boys), were not very good.
I believe Neil Sedaca had the No.1 song in the country the night we heard those memorable words by Ed Sulliven,
"Ladies and gentlemen, the Beatles!"
That's when the world personally changed for me. I was 7 years old and before the night was over, I threw out the butch wax and was trying to comb my hair over my eyes.
But after that, people got used to that and the Beatles music got more complex. Then, just like before, coming out of left field, you hear those first few chords of Purple Haze and wham, you start hearing sounds you never thought a guitar could make. You saw things being done to a guitar you never imagined anyone would do. I mean, when was the first time you saw a guy **** his guitar on stage; or play it with his teeth; or behind his back; or while doing summersaults; or lighting it on fire in effigy?
There was a saying that Hendrix was the first black man, attractive to white women. He blew the socks off Clapton, Beck, Townsend; that's not a cliché, that's what those people actually said. After Hendrix, music became more hard and driving. And consequently, we started getting bands like Led Zeppellin, Black Sabbath, Deep Purple, Ten Years After, The Cream, etc.
Then the '70's came along and everything sucked. The only good bands during that time were the Eagles and Zep.
The '80's weren't that good either. You had The Boss, but you also had all those "hair bands". Way too much glam. And what came out of that?
Grunge!
Nirvana was the anti-hair band band. The played in t-shirts and billybong shorts and sang songs that were protesting against the status quo. And just like all the others, we start getting bands like Stone Temple Pilots and a bunch more I don't even know the names of.
Disclaimer: In no way was I inferring anything detrimental to Guns n Roses. I know they were a great band.