The idea that Spielberg brought down the quality of mainstream Hollywood product is a myth. It’s belied by the fact that the most popular films of the early 1970s were cheesy disaster films like ‘The Poseidon Adventure’ and Mel Brooks films. Jaws was miles above that stuff. Close Encounters and E.T. were quite artful and display an independent vision. Ray Bradbury called C.E. the best Science Fiction film ever made. As for who made worse films than the two you mentioned, I don’t regard 1941 as a bad film...in its uncut version its an exhilarating cinematic vaudeville with a great sense of constant motion. And even the very best filmmakers have made duds, Hawks, Ford, Bergman, Hitchcock. If Hook stands out its because there was more attention paid to it.
I'm not sure I buy the argument. Nothing lasts forever in Hollywood. And the dramatic and sensationalist innovators weren't really opposing camps: someone like Coppola or Scorsese could bridge the gap between artistic and popular film. Maybe, in his own way, Spielberg could as well. But the argument can't simply be dismissed or ignored.