While some of the claims may be valid, this article is full of propaganda.

How can Telegram distribute messages in channels with more than tens of thousands users with P2P encryption? If there's 10k users, should Telegram store the same plain message 10k times simply because there's 10k public keys? If the sender encrypts and signs the message with 10k public keys, can the sender handle such a resource-hungry task? How can newly joined users decrypt old messages?

Of course there's fishy things, but the unprofessionalism severely drags down the value of this article.