"It's their job to watch for threats both foreign and domestic."
Nope. Only NSA domestic tasking is to develop secure comms and crypto for use by military and State. Like CIA, they are forbidden to do deomestic intel gathering. By law, anyway.
Everything I've read in the past six months indicates that less than half of what he took has even been released to Greenwald et al, and they've released but a portion of what they're working with. But maybe you have better sources (no, that's not snide; you're a sharp cookie when you're on your game, so maybe you read something that I didn't.)
My understanding is that the purpose was not particularly to 'expose the NSA' as to expose such things that they are doing that are counter to, or an un-authorized expansion of, tasking, and done in violation of the several laws that apply, and perhaps, even likely, of the constitution under which those laws operate.
I mean, c'mon, while I know that Bamford's "The Puzzle Palace" was news to some when it came out back when, but the essentials of the basics of what the various intel agencies were doing was kinda obvious, not to mention stated outright in public documents. So long as there was no drama, things just went along quietly, is all. Thing is, going back to Church et al, historically those same agencies have a recurrent problem with both mission creep and off-the-books activity.
I'm enough of a realist to figure that there are some gray areas; that things can get nasty in the dark corners. But that's a long sight different than the wholesale vacuuming of every domestic electronic comm up to garage door openers. So far as has been reported, despite repeated questions from Congress, so far no information on terrorist activity leading to its disruption that could not just as easily and readily and legally be obtained by heretofore existing means and methods has been given. Further, claims to the contrary, no one has been shown to have been harmed by the disclosures, although certainly some reputations and business deals have been affected.
Look, I have no particular axe to grind here. I mostly tend to favor law and order; the right to privacy, the right to speak, the right to peaceably assemble, all without chilling consequences stemming from total surveillance.* I also tend to look with disfavor on over-reach and skullduggery. Quaint tho it may be, especially given the hypocrisy and, some would say, the corruption of Congress, I really don't like it when public officials lie to the only body that ostensibly is looking out for me, either.
*(Btw, I recall few if any contemplating the heavy psychic load and attendant mental health problems that arise in such a state. (You ever talk to someone came out of East Germany? Not pretty.) We're already training our schoolchildren to accept such things as being arrested, handcuffed, and taken to jail from out of a fifth-grade class for doodling with a dry marker, along with invasive searches and withholding of needed medication; the list goes on. Then we have college free-speech zones requiring a two-week reservation and approval. Say what? That would have been popular in '70. Bad enough children have no childhood now; far worse is molding them to compliance with a totalitarian state by high school. Heck, looking back, I and most of my classmates would have been imprisoned or dead by fourth grade, way things work today. The times are not that different, but our collective heads are sure twisted up pretty bad to let this shit come to pass and think it somehow good and "justified". Only IMO, of course.)