If he'd been smart enough to send the war crime data, and ONLY that, to the Hague etc then he'd likely have fared better than by doing a bulk data dump which included so much material he couldn't have checked it all.
You're correct. He would have been caught after sending only the first handful of reports, and he probably would have been tried for only one count of espionage instead of six. And any actual crimes that folks might have uncovered in the rest of the material would never have been uncovered.
That's the problem. At a fundamental level, whistleblower protection must cover public disclosure, because (with the exception of a single isolated incident here and there) if the organization against whom the whistle is being blown were capable of policing itself, the blowing would not have been necessary in the first place; blowing the whistle to an internal auditor is pretty much guaranteed to be useless. And once you release something to the public, chances are, the government knows who you are. Therefore, you get one shot at releasing everything that needs to be released. Anyone suggesting that there's another way is really kidding himself or herself.
This is not to say that he couldn't potentially have tried to be more selective about it, but there's also a time factor involved. The longer it takes from when a crime occurs to when the public knows about it, the more likely it is that the perpetrator will get off because of statutes of limitations. Therefore, if the goal actually is ensuring that those crimes get prosecuted, the best hope is distributing the information broadly to a large group of people who can then divide and conquer. The press is remarkably good at that. The only question is whether they can be trusted to be responsible about what they disclose.
Now disclosing it to a site like Wikileaks... is a different story. His mistake was not what he disclosed, nor was his mistake disclosing it to the press. His mistake was disclosing it through a dubious organization that operates on the fringes of the law rather than going directly to a reporter at a major news organization.