... look at the Hugos from their start up to the start of the Nebulas -
The Demolished Man, Double Star, The Big Time, A Case of Conscience, Starship Troopers, A Canticle for Leibowitz, Stranger in a Strange Land, The Man in the High Castle, Way Station, The Wanderer, and
Dune ... all these books are still esteemed and most are still read and discussed and considered not just good books, but great. Bester, Heinlein, Leiber, Dick, Herbert, all still huge and Blish and Miller still right behind, even with Miller's small body of work (and Blish's not-huge). Simak may be fading but is now frequently mentioned as someone who should be mentioned more frequently.
And compare this to a Scalzi fanstroking joke, a Willis mess, a couple of first novels, four fantasies or so, an arguably lesser Vinge, a somewhat mainstream lit book, etc. for the last ten. Not a whole lot of these are discussed even now, compared to the discussion about books from a half century or more ago.