All server side software is proprietary as you don't control it. With that being said having a centralized design isn't great but Signal is well known and pretty well proven.
There are other messagers but don't though Signal out so quickly.
Molly still depends on Signal's centralized servers.
Best solution I know of currently is SimpleX, though Veilid (and VeilidChat by extension) also seem promising, though it might take a while for those to be usable.
I don’t think you know how many commercial use cases are relying on XMPP, nor how much the community has been working on updates. Older technologies tend to have maturity is spec but also in implementations where the servers are robust & already at the point of optimization over chasing features. We see this with how little specs it takes to run a server & have Conversation forks on Android have some of the best battery life & data plan usage in the chat space. The network is massively decentralized too… unlike Matrix where almost everyone is on Matrix.org or a server provided/hosted by Matrix.org giving them all the metadata.
Tbf not all the chats being E2E encrypted is a UX compromise. It makes Telegram a lot nicer to use across devices and allows just accessing your messages from anywhere without needing your phone to be on. Plus no need to back up chats etc. because they're all just on the server. As opposed to secret chats, which of course are bound to one particular device and can only be accessed from there.
I'm all for E2E by default but I must say I actually like the idea of having a choice in this particular case.
There's no reason for secret chsts to not be stored on the server and to not be synced to all your devices. We've had double ratchet for a while. Telegram rolling their own crypto is dumb for many reasons
Correct me if I'm wrong, but even with double ratchet, retrieving and decrypting the message history is tricky / impossible, no? Afaik signal does allow you to receive new messages on multiple "linked devices", but a new linked device doesn't have access to any messaging history.
From a privacy POV, sure, not trying to argue that. Just saying that Telegram does have a bunch of features like that that wouldn't really work if all chats were always E2E encrypted, so there's a reason that it's opt-in. Whether it's a good one or not is up to you to decide for yourself.
Though I definitely think that Telegram could do a much better job explaining the trade-off, especially in a world where many major messengers are always e2e encrypted, and people somewhat expect it to be the default.