Tolkien's another obvious example - lots of little stories and books and things, but his eye was on a grand English epic.
Art Spiegelman - did lots of weird alt comic, but then also made his massive glorious Maus.
Maybe it's always been unusual but I'm somewhat disappointed that you don't see more of this sort of thing. Like, people who make solid sitcoms for years but never even try to make a lasting glorious comedy.