Neither were some giant secrets, and were previously dismissed as unsubstantiated rumour. Hersh collected enough factoids together to substantiate them enough to become a news story, rather than a military legend.
Most notably the AP in 2003, a year prior to Hersh's reporting. 60 minutes covered the Taguba report before Hersh's article was published online.
https://en.wikipedia.org/wiki/Abu_Ghraib_torture_and_prisone...
Yes, but critically, also not the last. Other journalists corroborated, more sources came forward, evidence, hearings, photographs, convictions.
He deserves credit for his excellent, Pulitzer Prize-winning work covering My Lai. But to my knowledge he has never once been the first to report on a scandal and been right about it.