Earlier quoted context omitted.
This is a bizarre take. What's considered "serious security" depends on the needs of the person and the kind of info they're transmitting. To tell people that there is no advantage to use Signal instead of much less secure alternatives because your Area 51 security requirements aren't met is actively harmful and bad advice.
LOL, "Area 51." Whether Signal or Telegram, you rely completely on trust in the central third party for security. The choice of whether to use Signal or Telegram should depend on which of these organizations you trust the most (their leadership, their internal employees, and their security from external infiltration), NOT based on what technology they use in the client & server. But you simply shouldn't use either be…
This is technically correct but not in a way that matters. Signal pushes everyone to depend on Google to distribute the software. Through this system, it isn't even just Signal, but also Google and anyone who breaks into Google that can inject a compromised client.
You don't know that the client on the other side isn't getting its Signal app through Google.
More importantly -- even if you DO know the client on the other side -- the WHOLE POINT of Signal is this massive network effect where you don't need to coordinate with the other side.
If we're talking about the much smaller network-within-a-network of users who installed Signal from a non-Google source -- it's no longer compelling. Why bother with it? Less error-prone to get both sides to set something else up.