People who love the Telegram affordances wish that the platform would also suffice for intimate messages. Why have two platforms, two UX's, and (most importantly) two user bases? People who live Signal wish the other thing.
But you can't have both. They are incompatible design spaces. Telegram's security story is atrocious. It's best compared with Slack, not with Signal. If you're looking to compare a serious secure messenger with Telegram, look at Matrix, which has many of the same goals.
It is important that there be a messaging platform in common (if not universal) use that is fit for purpose for secure messaging when it really matters: when the compromise a message could cost lives or fortunes. Most "secure messaging" is LARPing; it doesn't matter if the "E2EE" in a pseudonymous 500-person chat room is secure. By all means, make it harder to dragnet that channel, modernize the protocols, whatever. But you can see right away how little security really matters to these groups, whether they're on Telegram (with no group security) or Matrix (which at least tries), because messaging app affordances are all people talk about with them.
Its security is questionable but it gets users by the boatload anyway because it doesn’t consider any platform an afterthought, they all get first-class treatment. Other cross platform messengers would do well to embrace a similar philosophy.