Well, I can't choose for you or your peers, but you can say to them those who have looked into it, think iMessage is a security nightmare and there are better options that help you all sleep better at night.
It's not that Telegram started being good, it's that the experts felt it was so bad they decided it was for the public good to give pro bono advice on the topic and didn't feel too strongly about advocating wrt the matter ever since, aside occasional social media chuckles when more vulnerabilities in Telegram have been revealed.
Sure, all messaging apps have problems, bugs, and issues, but with some there's clearly more effort in building a foundation that's not accumulating technical debt like there's no tomorrow. If Telegram suddenly wanted to enable E2EE, they'd have to start from the ground up. You can't glue E2EE on top. So when you look into the software engineering aspect, you're inclined to look into how the product was made, and the design rationale. None of that holds water for Telegram. What you get is something that on paper looks exactly like FB Messenger, and a bunch of promises to never abuse the access to the insane amounts of private data that accumulates.
I've been looking to secure messaging for a decade now and Signal's by far the best option right now. Threema is pretty good, and Element's getting there, although it needs more time to mature. You were already using Signal, abandoning it wasn't perhaps the smartest thing to do: Downtime is of course very unfortunate, but I've had more outages with Telegram than with Signal. Also, again, it's easy to fix a broken window, much less easy to rebuild due to rotten foundation.