(Also, calling PGP "the best encryption there is" might be a bit of hyperbole.)
And the company's business model is absolutely irrelevant actually. You still need end to end encryption.
> "But then will your diary service work right with it?"
Yes, it's called an email archive. It's searchable too. All you need is an email client that supports PGP. I personally use Mailmate.
And I've got email going back to 2004, while I no longer use any apps or online services from 2004 (most died).