Earlier quoted context omitted.
He's in "I want corroboration" territory for me. The big scoops - My Lai, Abu Gharaib - were backed up with hard evidence and other organizations confirming the allegations. Stuff like "the US faked Bin Laden's burial and chucked chunks of him into the mountains" have, thus far, not been.
Abu Ghraib happened, and My Lai happened, and Hersh was first who brought these two stories to light. 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.
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.