Only leak the files that are relevant.
* Removed the target from his back. At this point, all his value is "to be made of an example" not "a former operative with incredibly sensitive information, potentially worth neutralizing"
* Recused himself from being a political player like Assange wanted to be.
Also, who says he is a good judge to make the right call for each document?
Journalists can do a far far better job of responsibly handling the material, with enough time, resources and expertise to investigate the material, even get in touch with the government, etc.
Doing it personally would've been incredibly irresponsible and actually a power-play for personal gain not whistle-blowing for the better.
One might argue that any damage to intelligence interests is superceded by the public's interests in learning about abuses, but had he made a more targeted leak collateral damage might not have been an issue.
Trusting journalists to do the job is a cop out. He took the action of taking the documents, then foisted responsibility on someone else. And make no mistake, intelligence services spy on journalists and have compromised journalists. Snowden had no way of knowing whether other intelligence agencies could get to what he gave the various media outlets. Even some carelessness on their part could have revealed secrets to others.
It was Chelsea Manning who a did dump without reading them first.
Imagine that the year is 1942 and someone leaks you a stack of bookkeeping records from some german labor camp in poland. In it, the records account for gassing prisoners by the truckload, but to your eyes it's all just just the cryptic numbers and administrative filler of any complex bureaucracy. To make any sense of it, you need many layers back of the surrounding documentation-- not just to establish what you're looking at, but to establish what you're not looking at. Communication that shows that the data is real, not an exercise, that the prisoners are being killed rather than that the accounting is just covering deaths from natural causes, that it's really a big intentional program sponsored from on-high and not just a fluke where a local administrator or two went nuts.
Without a wealth of supporting material it would be easy to dismiss Snowden's reports as "sure well, there was some overreach here and there. It wasn't officially sanctioned and the relevant parties have been sacked, James Clapper had no idea and did not perjure himself and we haven't been systematically lying to the public for a decade." In a world where the NSA was accountable to the public, Snowden would only have to reveal enough to force them to account and disclose and continued inquiry would unearth the rest. But we do not live in that world: The NSA's actions are not open to public inquiry. One shot is all we got for any real transparency into the mass surveillance apparatus. Consider the byzantine dismissals that Jewel v. NSA experienced. ( https://www.eff.org/deeplinks/2019/04/judge-dodges-legality-... )
It seemed pretty obvious to me that Snowden purposefully obfuscated what documents he took by accessing everything-- a fact you seem to have exploited in a number of posts to exaggerate the scope of the documents he took, according to our best understanding of his actions per the journalists he worked with-- in order to create a situation where the administration's ability to tell additional lies to cover up the situation would be limited by the risk that somewhere in the stash Snowden had a document which blew the latest lie apart.
For another example: There is an absurd number of patents filed on most of the technical tools being used for the mass surveillance on the internet-- and their feature sets often end up leaked in product documentation and internet standards. They're not even particularly well hidden, some with co-authors who's linked in pages brag about their TS/SCI and work in intelligence... Yet, pre-snowden, people pointing to this wealth of details even combined with first hand accounts of how it was deployed, were just treated like kooks. Without the ability to open a real inquiry it isn't enough to prove that something suspicious is up, the proof must be utterly overwhelming to have a meaningful effect.
Norwegian newspapers backtracked and apologised for writing articles exposing Norwegian participation in illegal metadata monitoring, arguing that the monitoring that for all of the other parties involved was about domestic monitoring in Norway's case for some reason was about Afghanistan.
Had it not been for the amount of surrounding context, the lies would have been believable. Even then it took the then head of military security to step up and make claims about operational issues in military security that they never talk about, to draw attention away from the vague denials of the police security service.
But the sheer amount of data, coupled with the revelation that the US itself captured full recordings of the same conversations that Norwegian surveillance supposedly captured valuable metadata about made it stand out as a ludicrous cover-up.
And still the newspapers did not dare challenge it even with all the extra details.
As it stands, Snowden released too little - even with all the material he did provide, it was still something that proved possible to sufficiently deflect from that it had shockingly little impact.