This is essentially the Google model. Your search queries and browsing history (and Android and Chrome) are essential to targeted ads shown on every website "the webmasters choose to enable them on".
What? Google uses all your info for creepy personalized ads. Telegram is showing the same ads to everyone in a channel. And it isn't in 1:1 chats cuz they're supposed to be non-intrusive and gives a feeling of privacy.
Who is the 'maintainer'? Telegram is the only entity here.
https://gizmodo.com/the-dangers-of-techs-privacy-promises-18...
How? Google has all the whatsapp chats via the drive backups which 98% of users enable. fake E2EE
Telegram has an open API, alternative clients and free cloud storage.
They explain very well why they didn't want to give misleading e2ee claims like whatsapp https://telegra.ph/Why-Isnt-Telegram-End-to-End-Encrypted-by...
It is open source.