I disagree with this. A point the FAQ didn't mention is user psychology.
Technically, the correct way to use e2ee chat on both Signal and Telegram is to verify the key fingerprint using a secure channel separate from Telegram. In reality, few people do it, so the default makes a huge difference.
If all of my Signal chats are e2ee by default, and I operate under the assumption that most if not all of my chats are encrypted and secure by default, when a chat that really needs to be secured comes in, I wouldn't think of verifying the fingerprint in a separate channel first, because Signal didn't train me to do so. If it did, Signal would have been a lot more annoying to use, because it'll have to pop up warnings and all that.
Enabling e2ee in Telegram is an explicit act, which means that what that mean is enabled, I know for sure I need to make sure it's really secure, and it will trigger my memory about verifying fingerprints. I would argue this trains the user to think more about operational security instead of just theoretical information security.
As far as I can understand, Telegram's secrecy by default is __good enough__. They control all of their data centers and internal networks, and they have been known to refuse to comply with government orders. Given that I continue to use Apple and Google services with similar or lessor guarantees, I consider that good enough, and I'll choose my messaging app based on secondary factors such as usability and features. Telegram wins hands down in these areas.