Shawshank Redemption was a book. The Godfather was a book. Lord of the Rings, Forrest Gump, Fight Club, Goodfellas, Silence of the Lambs… That’s just from the first 25 of IMDB’S top 250.
From the top 10, only Pulp Fiction is original and not a sequel. If you go to the top 20, you can add Inception, The Matrix and Se7en. That’s 4 out of 20 (or 1 out of 10). There’s a lot more original material beyond the top 25 though, but your point that every great movie is a “ripoff” very much stands.