WhatsApp is owned by facebook, the telegram team is not very loyal to the government, Telegram can send huge files. Telegram has end2end encryption disabled by default and it does not work across multiple devices. (How is whatsapp here? does it even have a Desktop Client?)

Your points still stand true though.

Thats like remote play, not a desktop client.

How is it remote play? It is a full web client.

Turn off your phone and lets see how that "full web client" behaves.

E2E with multiple clients is clunky at best.

Why? should be so easy to just send it once per device.

That might work for incoming messages.

* How does your history get synced when you send a message?

* What if some of your devices are offline?

* What if you have two devices that are never online at the same time?

* What if a device is offline for a very long time? (No possibility of holding the message on a server for eventual transmission.)

* What if there's only one device currently on that receives a message and then is destroyed?

Marking a single device as the master and forcing all other clients to proxy through it removes a huge amount of complexity.

The entire Telegram encryption protocol is open source. So are the apps.

The only thing closed source in Telegram is the server software. Everything else (apps, protocol,...) is open source.