I have a bad feeling that this will not end well if it's left to run its course.
What happened to the days when people just took a chance and tried something new and waited for the results to come in? What do they have to lose by giving Mastodon or the Fediverse a try except a certain amount of time and effort? The idea of having to analyze everything and scraping data from user bases before making a decision to freely jump in and give it a try is getting a bit absurd.
This is a great point that you bring up. I subscribe to an IRC channel that has bridges to both Telegram and Matrix. My feelings at this point, is that the weakest link is going to be of the most concern. But how all this technology interoperate with each other and how they actually handle privacy/security together is a question I cannot answer.