[zahllos]

End to end could still be default for 1-1 chats. Multi device support turns this into a small group chat but it is doable (Wire did it this way afaik; I think Signal does too).

Small groups could likewise be supported.

I take the point that for large groups client fan out of the double ratchet doesn't scale. We now have MLS but we didn't. There's also an argument of how can you really keep a secret in an open group of a few thousand people.

But on a small, "personal" level, e2e could absolutely be done. Not doing so is a choice, one that conveniently ends with almost everyone's chats stored on servers somewhere.

I would go so far as to say I bet telegram is a goldmine for TLAs.