Strongly disagree. The point of Signal is not just that it's encrypted. The point is that the source code is GPL and the service is free. Holding up a bunch of closed-source, proprietary, for-profit applications as examples of success only serves to obscure what should be the real goal: decentralized, anonymous, metadata-less, encrypted communication that anyone can easily use. Signal could be much closer to that goal but OWS & moxie refuse to allow decentralization or anonymity for bad reasons.
You are describing what should be the goals in your opinion, not the one of Signal's developers.
Having something that works to show (Signal), was a big point to sell to those, closed and already used by many people, systems; so having a non federated Signal means they can iterate more often and change things how they more or less want.
In the long run federated protocols and servers demonstrated their resilience regarding third parties and time, see irc for example.
Probably Signal is just a reference implementation, the big deal is implementing Signal protocol in different systems (whatsapp, allo, fb messenger..).
Having said that, I would be happier to not give my phone number for registration, and contact discovery but this is today a user interface well understood and accepted outside geek communities that's hard to eradicate.