This is similar guarantees that a lot of other chat and VPN companies offer. Personally I would consider any information given out to a company non-secret, especially to those operating outside my jurisdiction.
No, we have the fact that they don't collect it in the first place. The whole point of the Signal design, reflected in the published source code, is that the server doesn't need this type of information and so it isn't sent to their server at all.
As Thomas explained this takes a bunch of extra effort in the Signal design, hoop jumping that normal users will never appreciate. Moxie believes this is worth doing, although I think people's constant cynicism is gradually wearing him down or maybe that's just the jetlag.
If you tell me and Alice and Bob your real name, and then it's leaked to the press, I guess I sympathise if you distrust me as a result even though Alice is a famous gossip.
But if you only gave Alice your name, and then you distrust me because she sold it to the press that makes you a crazy person. "It could have been anyone". No, it couldn't, it was Alice. She's the only person you gave it to.
So the logic you're using here is essentially: "since we have to take Signal's word for some part of this, we might as well use services that promise the exact opposite". I don't find that argument persuasive, but you do you.
Oh, and I forgot, you do need to essentially blindly trust Intel.
Also, Matrix offers a possible alternative.