Signal will allow traffic analysis. You send the message to signal, if they wish they can write down to whom they send it on.
It is impossible to make a secure system without the continuous transmission of dummy messages to large numbers of users.
Again: in every system there's always some kind of sleuthing you could do to attempt to identify a user. That's not the legal standard. The complaint against A/I is that they knowingly and deliberately assisted the PKK.
They don't have to do that because accounts are associated one-to-one with phone numbers.