Sorry, but no. Leaving aside the problems of definition, Science fiction is just a subset of fantasy where the fantasy elements are presumed to have a scientific basis. Science fiction says “what if we go to Mars”; fantasy says “what if magic existed?” Both genres describe fantastic events, and both are equally about ideas. You’re trying to win a victory by definition by defining fantasy to suit your point.
Then Heinlein didn’t write good SF, I guess. Nor did Bradbury. And neither did Harlan Ellison. Or Robert Sheckely. Or Alfred Bester.
I strongly object to this characterization of SF being scientifically accurate. That always took a back seat, and wasn’t even a concern until Hal Clement began to invent hard SF. To say that “hard SF is the only SF” ignores 75% of the field for a sort of science fiction racial purity that never existed (even Hal Clement was willing to ignore scientific fact if it got in the way of a story).
Explain the difference between “Buck Rogers” (which Hugo published) and Lord of the Rings. We see Buck going on an adventure filled with scientific wonders in order to defeat a villain; on the other hand, we see Frodo going on an adventure filled with magic wonders in order to defeat a villain. You could easily do The Hobbit as science fiction (Pat Murphy has – see her There and Back Again). You just see magic vs. science and don’t note the underlying similarities.
On the issue of the age of authors, one point is that SF writers break in later than they used to. Other then Ted Chiang and, further back, Terry Pratchett, there are no teenage SF authors like Asimov, Pohl, etc. Chip Delany broke in around the age of 20; William Gibson – who Chip has called his literary grandson – broke in around 40. As Delany said, “Grampa and Grandson are almost the same age.” Since SF writers break in later, they are generally older.
As far as good news, there is a chance that the real place for science fiction is in the mainstream. Look at Jasper fforde’s Thursday Next novels – popular, and clearly SF (unless you want to be tightassed about your definition). He uses SF tropes along with fantasy tropes and creates a wonderful amalgam. There’s also Christopher Moore, who isn’t listed in SF, even though some of his books (most notably Fluke) clearly are. Neither author is shelved in science fiction or fantasy, but they seem to be doing quite well.
So the long run salvation would seem to be entertaining stories that use SF as a basis for their plots, but which don’t insist on being 100% scientifically accurate, and – like Heinlein or Bradbury – are willing to ignore science in order when it gets in the way of a good story.