Telegram supports open source and third party clients, so if you wanted the benefits of E2EE with a popular chat network then that's a better way to go. Custom clients on the telegram network.
It is best is to use something like Element/Matrix though, for sure. But if you're trading UX for convenience then materially the difference really is a lot smaller than you imply.
By switching their optional E2E encryption from their weird proprietary thing to the Signal protocol, Telegram could at least display some goodwill – but only making that the default would show that they actually care about their users privacy.
I'd be happy if it was available on desktop clients as well :D
The desktop client requiring me to constantly have the mobile with me defeats the purpose.
Still... It's an excellent product. Default e2ee, notifications on partner key changes. The main thing I'd like from it would be an option to block me from sending messages until I reauthenticate the partner, or a colour coded system like threema that serves as a reminder that without authc you really don't know who you're chatting with.
We already had that with OTP over ICQ/MSN/AIM etc. in the early 2000s. I could use it with about all of 3 other people.
And why stop there? You can always message base64-encoded PGP messages back and forth. Problem solved!
Except that defaults matter.
Also, both iMessage and WhatsApp support encrypted cloud backups.
Its not like its a significant difference honestly. I know people beat the E2EE drum and they definitely should: but that only makes sense if the clients are disconnected from the transport. IE: ensuring that collusion between them is less possible.
Though storing things on the server is something telegram then has to secure on your behalf, it does provide a tangible UX improvement.