I think that Snowden leaks were more or less an open secret. I mean, it is about spies spying. Sure, the NSA overstepped its borders, but it is not exactly the first time (remember ECHELON), and the way it did that wasn't revolutionary. They didn't have a quantum computer, nanobots or anything like that: just competent computer security specialists and too much money to spend. Not even something significant like breaking commercial-grade crypto or anything like that, they "broke TLS" by inserting wiretaps in datacenters where data wasn't encrypted.
Snowden gave proof and technical details about what was happening. It is like showing proof that Israel has nuclear weapons. Israel doesn't talk about it, they may or may not have nuclear weapons, most people think they do, and such a revelation won't surprise anyone, but it is still a big deal, because they can't use their "deliberate ambiguity" strategy anymore.
I was working at Google when it came out, and that they were tapping our private inter-dc links was a huge update. Before I think it was something like "I guess the NSA could do that a bit, but it would be a prohibitively costly to do much" and then suddenly it was "we have to encrypt all of this as quickly as we can". There was a huge internal reprioritization.
(Speaking only for myself; I didn't work on any of this directly)
Consider that Wired reported on NSA's secret mass-wiretap of AT&T communications in 2006! This was a high-profile lawsuit (Hepting v. AT&T), which was dismissed in 2009 after new immunity legislation in 2008. That was followed by Jewel v. NSA in 2008 which seems still unresolved.
Not to mention the whistleblowing on the Trailblazer Project and New York Times reporting on the "Terrorist Surveillance Program" in 2005/2006.
I became known as a conspiracy theorist amount my friends when I told them about this. A week later the Snowden revelations came out and yet somehow I’m still the conspiracy theorist.
I went out drinking once in DC with some people who worked at the NSA in 2005 or so and they said they were hiring for people to analyze "all the traffic on the internet".
When the Snowden leaks came out it was not a surprise. Granted most people don't go out drinking with the people doing the spying, but even people who work at the NSA can't keep a secret, if it was even meant to be a secret.
Snowden gave proof and technical details about what was happening. It is like showing proof that Israel has nuclear weapons. Israel doesn't talk about it, they may or may not have nuclear weapons, most people think they do, and such a revelation won't surprise anyone, but it is still a big deal, because they can't use their "deliberate ambiguity" strategy anymore.