There are obviously other CDNs (or whatever Cloudflare considers itself to be these days) and other certificate authorities. They are all interchangeable thanks to open protocols (HTTP, TLS/ACME in this case). Contrasted to Signal: there are no other implementations.
Re: Signal, it's even worse: they are openly opposed to federation and to letting alternative clients use their server. They demand control and obedience, which has always been suspicious-enough to defeat any goodwill effort on their side. Why would I have/want to trust them when XMPP is a viable federated alternative?