This statement is simply false, Telegram has never claimed group chats are "end-to-end encrypted". Only secret chats are claimed to be and proven to be.
Your refutation of my claim is an article that claims Telegram's use of TLS encryption makes it more secure than its competitors, and links to another article going into even more detail about that ridiculous claim. I feel comfortable with where it leaves my argument standing.
The central point of your comment was false and invented. You have claimed they made assertions they absolutely never made.
I don't see how the TLS claim is relevant, your comment is still wrong. It also misrepresents their argument, that competitors using cloud backup is less secure than not doing so because it introduces a very untrusted third party (Google Drive is not E2EE).
Their claim that E2EE + Google Drive backup is not secure seems pretty valid to me, not that it's related to the inaccuracy of your comment (it's still a false statement, and pretty egregious considering it's never been claimed).