Unlike whatsapp and signal, telegram private chats are not synchronized. So if you lost your phone and started a new one, the chats will not magically recover as in whatsapp.
That's not true. Signal stores all messages on device.
or do you mean that encryption is not enabled by default in every chat? This is not an indicator of the messenger's privacy.
Encryption on Telegram only works in 1 on 1 chats and is turned off by default meaning no one use it.
Signal have been blocked in several countries including Russia and Telegram has more users there and it isn't blocked.