Hi Romain,
thanks for you compaison and I share your thoughs of about the threat it is to use unsecure messaging services since we are sending our private conversations through them. But today we don’t only have Signal as alternative — there is also Wire, a swiss-german startup which offers encrypted video-, audio- and text-chats (also encrypted bots) based on the Signal-protocol, the code is also open sourced on GitHub, native apps for different devices and there is also Threema which offers encrypted text chats and some other functionalities but not open sourced.

Some months ago I tried to bring my friends to Signal but they did not like the app and later on I discovered Wire and I tried it again with my friends and they really like it because it’s a fresh new messaging app and it’s highly secure, too. And there are some other reasons, too why Signal is not THE SECURE messenger: Signal still uses Google Cloud Messaging, your contact list is not private and you need a phone number to use (impossible in states with no option to buy prepaid SIM cards without registration, e.g. Italy).
Here is a good blogpost about it or this website about secure messageng apps.
Today I am mostly using Wire for my communcation with friends where I can feel safe and have a great app on all my devices to chat with.

So in short: there is not only Signal in the universe of secure messaging services. 😊