It is false that chats are "unencrypted" (I know, it is repeated on every submission about Telegram here but it does not make it true whatever Goebbels said). Here's a quote from the FAQ: "The relevant decryption keys are split into parts and are never kept in the same place as the data they protect. As a result, several court orders from different jurisdictions are required to force us to give up any data." https://telegram.org/faq#q-do-you-process-data-requests
That is only true for the End 2 End encrypted chats, which are a separate and not very user friendly thing. Regular chats and group chats/channels are by design unencrypted.
Then it is not correct. A security analysis of Telegram has raised doubts about their e2e before. They have (had?) a blogpost up where they pontificate about how it not necessary and would put a burden on their channel feature anyway.
The security analyses I am aware of target MTProto 1 which is not MTProto 2 used for quite a number of years now. MTProto 2 uses standard security primitives.
You cannot say "it is not correct" without proof. We know all messages not just E2EE are wrapped in encryption on their way out a Telegram client and we know they are decrypted on their way in because client source code is available.
Why don't you have a look for yourself then let us know if you've confirmed your suppositions?