All parts of Signal are free software, whatever possible future direction the organisation takes is fundamentally irrelevant. Whatsapp is and has always been proprietary and could therefore never be trusted.
Matrix is great, but it’s so complex that you can’t recommend it to people just looking for a Whatsapp alternative. It isn’t even encrypted by default, and in fact it isn’t meant to be, it’s more like a modern version of IRC, with a focus on huge group conversations anyone can join. Additionally, federated networks, whether they’re Matrix, email or even XMPP, all suffer the same problem: 99% of all users are signed up to the same server, and you have to blindly trust any server you don’t host yourself. Pretty much everyone on Matrix is signed up to matrix.org (so much so that when matrix.org is down, people believe ‘Matrix’ is down) and pretty much all email users are signed up to Google or Microsoft’s email services. In fact, the email situation is so dire that many (non-email) services don’t even allow you to sign up if you don’t provide a Google/Microsoft email address. So, even decentralised networks tend to unintentionally move towards a strongly centralised model.
Which server would you suggest new Matrix users sign up to? Your personal one, which isn’t always online and isn’t kept up to date all the time, or the big one that rarely goes down and supports all of the latest and greatest feature? Which client would you recommend? Your minimalistic client of choice, which is developed by a single person and doesn’t support many features but fits you personally, or the big one that’s developed by a whole team, supports all of the latest and greatest features and gets constant security patches?