"attacks" seems like a hyperbole here. From the way I read it, Durov was simply stating facts and there wasn't any ridicule/rage attached to his statements.

Atleast WhatsApp is end-to-end encrypted unlike Telegram.

I think Telegram is pretty secure, given that some nations want or have already attempted to entirely block it to prevent its usage by citizens.

Without end to end encryption? Not really. Mosty relies on "trust"

Secret chats aren't 2e2 encrypted?

I looked at their sceme and can't figure it out. How does T's regular scheme work - server encrypted? That wouldn't make much sense :-)