I think it is becoming harder, if not impossible, to "invent" new music.
When I heard Beethoven in Steppenwolf as a child, I was sorely disappointed in my "favorite band" and my dad's country music was full of Rachmaninov, Wagner, even Gombert, Vivaldi and other "intense" themes. I hear Mozart, Handel and Verdi in Black Sabbath, Iron Maiden, Alice Cooper, Korn and Pantera, Paganini, Schultz, Danzi and Handel in Blue Oyster Cult, Godsmack, St. Vitus, Motorhead, Disturbed ....... and The Beatles, The Who, The Doors, Jefferson Airplane, Hendrix, Led Zeppelin, Deep Purple and Eric Clapton are everywhere and have mostly used just about everything between them.
I don't think of it as plagiarism, though.
There is nothing new. There are no new ideas. There are no new themes. There are no new sounds. There are only new ways of making and combining those same old sounds, themes and ideas.
I hate it when people say that music is dead!