All of these are features a rouge client simply can ignore.
1. On one hand it takes away a nive selling point.
2. On the other hand it feels safer.
3. But then again - as a sw engineer who cares about security - I expect it to fall flat if someone decides to reverse engineer the official client and patch it to store everything to a database.
4. But then again, if they store it to an external db, what is to prevent them from storing random info, i.e. making things up?
5. Finally. If someone really wants to leak your data, what prevents a dedicated attacker from photographing every snap, confidential gmail message etc?
You don’t need to reverse engineer because the protocol is documented and the clients open source: https://github.com/peter-iakovlev/Telegram-iOS
If telegram was serious about privacy they’d make end-to-end encrypted chats default instead of a hard to use option and storing your unencrypted chats in their cloud by default.