But two issues - or call it 'differences in opinion' - in that article are relevant for me: The inability to use the service without a mobile number and federation.
I understand the rationale behind the former ("It's easier"), but I don't understand why it is mandatory. I could've been 1283783127356128531312 on Signal and optionally add my phone number to that identity for others to find me (and optionally let Signal use my contacts to search for someone). That could even be the default, opt-out during registration. But right now, I'm basically using my phone number, which I really hate to do.
Federation is probably hard to get right, and looking at Eric Lippert's "Every feature idea starts with -100 points" rationale I guess it is understandable that this isn't a thing. But I don't want to join another silo, even if it's the best of the crop so far.
For users like me, Signal, WhatsApp and yes, Telegram are basically the same thing, come with the same set of limitations and I feel that it is worth pointing them out from time to time. Just as the article did (I'm not agreeing with everything in there btw.)
People jump in to defend Signal whenever this comes up, but maybe that isn't necessary. Signal is a great project and most criticism I've seen here so far is not 'Signal sucks', it is usually more a long the line of 'Signal is not for me' and I have a hard time understanding why that is debatable or why this shouldn't be a valid position.