Re. originality in popular music, see this video. Don't miss the section starting at 2:39. This video by the Axis of Awesome is fun, too.
I'd thought the first video was going to be this one!
I'm sympathetic to the idea that pop music is decreasingly original & novel, but these videos are pretty slender evidence for it. The problem with invoking these videos is that they're sampling on the dependent variable: they pick out small subsets of recent country songs or recent pop songs which go together attention-grabbingly well. But precisely because they go together attention-grabbingly well, they're very likely unrepresentative of country/pop music as a whole.
(Also, even ignoring the unrepresentative sampling, these videos mainly just mean that particular chord progressions are popular. Comments on the Axis of Awesome video mention how the sketch plays on the fact that I-V-vi-IV is a popular chord progression, which it is. But that speaks only to harmony, not melody or arrangement.)
A lot of pop music today is difficult to distinguish from music made in the 1990s. The difference between pop music in 1960 and 1964 was much larger than the difference between 1990 and 2015.
Those claims sound likely on first hearing, but I doubt them more as I think about them. It's easy to have the wrong idea about what charting pop music sounded like in a certain year.
One can think of 1964 and imagine the charts were being revolutionized by a deluge of songs as memorable & novel as "You Really Got Me", but looking at Billboard's top 10 singles for 1964, I have a hard time picking out even half a dozen which stand out to me like that. (Admittedly, that's more than I can pick out from the 1960 chart.)
As for 1990, I surprised myself twice over! After I started thinking to myself along the lines of, "new wave and hip hop were well established by then, and I guess it wasn't long before grunge became a big deal, so maybe there was a lot from those genres?", I checkity-checked myself by pulling up Billboard's 1990 list. When I saw New Kids on the Block, Michael Bolton, Rod Stewart, Tom Petty, Aerosmith, I thought, "oh, wow, yeah, right, guess I was wrong".
But then I looked again and saw more. Janet Jackson's "Rhythm Nation" (Wikipedia: "incorporat[ing] dance-pop and industrial music, also using elements of hip-hop and funk rock"); Biz Markie's "Just a Friend"; Madonna's "Vogue" (Wikipedia: "a dance-pop and house song with notable disco influence" and "a spoken rap section"); Bell Biv DeVoe's "Poison" (Wikipedia: "in the style of new jack swing, a late-80s hybrid of R&B and hip hop"); Deee-Lite's "Groove Is in the Heart"; UB40's reggae-fication of The Temptations' "The Way You Do the Things You Do"; and Prince's "Thieves in the Temple" (Wikipedia: "a unique sound, starting quietly with echoed keyboards and vocals before the main section of the song booms in with a pulsating synth bass, syncopated drum machines, Middle Eastern melodies and opera-like layered vocals"). That last one's not on YouTube 'cause Prince and his record company are like super picky about people uploading his studio recordings.
It follows that my idea of the music crashing into the US charts in 1990 was patchy & incomplete. So who knows; maybe it is more different to today's US pop than 1960's was from 1964's? The test that'd answer that question would be taking a representative sample of charting songs from 1960 onwards and analyzing them systematically for diversity.
Come to think of it, I remember a paper — "The evolution of popular music: USA 1960–2010" — which has some relevance. The punchline?
We show that, although pop music has evolved continuously, it did so with particular rapidity during three stylistic ‘revolutions’ around 1964, 1983 and 1991.
1964 and 1991, ehh?
I'm interested in how people form valuations of the opinions of others. One domain to study is art. We have a long historic record of how the elite arbiters of taste have decided what artists and what artworks were great.
This is more relevant to 21st century American thought than many of you probably think. The defaults we assume, the stories that are told on television and in our movies, the things taught in our colleges, were partly determined by assertions made by continental philosophers and psychologists of the 18th through 20th centuries, most of which they just made up. [1]
The process by which philosophers eventually get their views accepted into the Western canon looks the same to me as the process by which musicians or painters are accepted into or cast out of the Western canon. Neither has much to do with the quality of the product.
For centuries, artists have been judged not so much by the quality of their work as by its novelty, and by its ability to raise questions while resisting any definitive answers. As one art critic wrote, "Probably more people have thought Hamlet a work of art because they found it interesting, than have found it interesting because it is a work of art. It is the Mona Lisa of literature."
Ironically, that was T. S. Eliot, just a few years before writing "The Love Song of J. Alfred Prufrock" and writing rave reviews of James Joyce's Ulysses.
I think novelty was the main criterion for artistic greatness by the middle of the 19th century. It was almost the only criterion, in all of the fine arts, by 1925.
But there is one artist who sticks out among the desperate attention-seeking artistes like an ordinary thumb: Brahms. Brahms accomplished something that, AFAIK, no one else had in any fine art, in all of European history going back to the Middle Ages. He made art in a style that had gone out of fashion before he was born, not ironically, not nostalgically, but because he liked it. As I understand it, Brahms was still writing symphonies in the style of Beethoven after Chopin and Liszt were dead. And his work became both popular, and accepted by the elite arbiters of taste into the canon, not for introducing any new style, but simply for being enjoyable. Or, as an unsophisticated ignoramus might say, good.
That would be analogous to a philosopher's ideas being accepted just for being correct!
Is that a fair representation? If so, why was he accepted into the canon, when anyone else who tried to just make good stuff would, I imagine, be laughed at or ignored? [2]
[1] Analytic philosophers were more rigorous, so nobody liked listening to them. There seems to be a Gresham's Law effect: The presence of bad philosophers who claim to have reached exciting conclusions without any nasty logic or math, makes it impossible for more rigorous work to get a hearing within society and the arts.
[2] I'm open to the idea that Robert Frost may be another exception, though I'm not aware of poems written in 1870 that could be mistaken for Robert Frost poems. I'll also note that people tried to stamp out appreciation for his poems because he wouldn't get with the Modernist program.