Telegram is almost on the opposite end of the spectrum of Matrix & Signal so I wouldn’t really consider it an alternative.

Their text explicitly acknowledges and waives away the security concerns for themselves.

How so? I genuinely don't know, despite casually using both.

Opposite end in terms of security. Telegram group chats have no E2EE, private messages aren't E2EE by default (you have to initiate it as a "secret" chat), and the encryption itself is home rolled.

Yup exactly, their home rolled encryption is problematic in and of itself, but the fact that it lacks E2EE means you shouldn’t even trust it in the first place.

They do publish https://telegram.org/blog/tdlib so couldn't a client author just do shared key encryption or something?

Also opposite in terms of feature-richness.

It also contains scam advertisement by now.

It,s quite clear what you never used it. UX wise it's one of the best clients and probably in the top 3 network-wise.

It's deeply insecure in most of the ways it is used.

But people don't care about security, that is obvious, they only care about UX

I should have been clearer in my initial post, but I was referring to the security issues with telegram rather than the UI.