Then Gmail is more secure than this service, because Google's servers are pinned in browsers, so you can't compromise them by compromising any CA in the CA hierarchy.

I don't really agree with this. Gmail is compromised by the NSA sending one email to Google.

I hear you dude but this is clearly not "end-to-end" encryption. End-to-end has a very specific meaning. End-to-end encryption means a messaging system in which one or more compromised node from node 1 to N-1 could not eavesdrop on the message. In this solution if you get access to node 1 (the server), you get access to the message. It's binary. There's either end-to-end encryption or there isn't. This one isn't.