"Truly secure communications" isn't all that matters when discussing email security.
There are meaningful differences in the scale of access. It matters whether the NSA (or China or whoever) can just read everyone's email off the network, versus law enforcement sending requests to email providers where they are verified to be legal. It's the difference between lawful access and espionage.
And then you realize that things like "providers opportunistically encrypting in transit or at rest" are largely irrelevant to having truly secure communications. You could have a conversation about "is Gmail less bad than Outlook.com" or whatever, but the whole point of the essay is that neither are meaningfully different if you have important secrets.