This is a very technology focused view. In any user system, the users themselves have to be a consideration too. I don't use most of them for the fact I don't have a smartphone. So for my use case, any chat application that requires one might as well not exist, so read the rest of this with that in mind.
People fall into a few categories:
- The don't cares. They use whatever everyone else uses, because that's what they need to use to talk to who they want to talk to.
- The open and defederated. If they can't self host, it fails.
- The anti-corporate. If it is run by a big organization, regardless of technology its a no.
- The technological illiterate. Basically the same as the first group, but if its not really user friendly they can't figure it out.
I'm sure there are others, but these are what comes to mind first. While signal might be the one that has the best technology for many that doesn't mean, and will never mean it is the "best" because their decision matrix doesn't weigh technology as highly as you, and their knowledge doesn't allow them to understand the nuances you talk about.