Just because there's only one email doesn't mean there were not substantial efforts made in other ways. Phones exist. Talking to people in person is a thing.

If you're going to leak 1.5 million documents and flee to China on the grounds of being a whistleblower after following proper channels, wouldn't you want to display some, any sort of proof that you indeed did attempt to follow the proper channels?

People claim this dude was a genius, make him out as some sort of tech/hacker savant, so why not make the slightest effort to show the world you really are a whistleblower?

We also have statements from Snowden suggesting that the reason he took the job was to gain access to those documents and them disseminate them to various world governments, which is a goal that would be impeded by whistleblowing through channels.

They didn't claim he failed to make an exhaustive effort. They claim he made no effort. That claim is demonstrably false.

If it's "demonstrably" false, you haven't demonstrated it yet. Can you point us to some evidence showing that he complained to any authority within the government about what he learned about NSA's activities? You'll need to show more than that he mailed someone; we'll need to know more about what was in that mail.