Salinger's reputation has as much to do with his short stories as his novel. A case could be made that Salinger's withdrawal spelled the decline of the American short story. Short fiction would never be as known or read or discussed or argued about after he stopped publishing.
The central character is whiny and self-obsessed. Holden Caulfield is a rebellious, nihilistic teenager. I consider it no coincidence that the Boomer Generation that grew up with this books consisted largedly of whiny, self-obsessed, rebellious, nihilistic people who never matured and remained teenagers for the rest of their lives.
Say that's all true. It's nothing new. Read Fitzgerald's early fiction. He's as whiny and self-obsessed as you could want. So was Thomas Wolfe (the Look Homeward, Angel dude, not the Right Stuff guy). So are most first novels. What made Catcher in the Rye memorable was the use of language -- very fresh at the time. Things also happen in it, too, in contrast to a lot of later novels.
So I don't think Salinger brought self-involvement and self-centeredness into fiction. Novelists and story writers have long been a very self-obsessed bunch. Affluence, the lack of real obstacles in life, university writing programs, and victim ideologies would have made fiction and the novel what they are now even without Salinger.
He did do a lot to bring the adolescent to the forefront of fiction for a while -- and a particular sort of teenager that hadn't been seen before. So if you want, you can give him a share of blame for what happened in the 1960s. We're far enough away from that now that it doesn't have to dominate our thinking, though.
Salinger also did a lot to give life to that urban romanticism of youth that Fitzgerald, and in a different way Kerouac represented. If you want to look for his heirs, maybe the films of Whit Stillman or Wes Anderson would be a better place to start than today's writing programs.
I'm not saying that Salinger was a man for all seasons or that his book would be something to take to a desert island for the rest of one's life, but more was lost when he stopped publishing than when he was writing.
Thank you for the thoughtful response.