It's probably unwise to think prosecutors and federal agents are stupid. They were in the 1990s crypto wars, but not now. What we tend to perceive as 'stupid' is in reality, 'powerful.' They don't need to explain themselves, because they put the onus of compliance on you. Gaming out the subpoena, Signal does not have this user information because it does not exist, but it does have server locations, 3rd party service…
To Mark Zuckerberg: "So, how do you sustain a business model in which users don’t pay for your service?" To George Floyd witness: "So you had something called a mobile device right? And a mobile device is capable of taking pictures right? And you used the mobile device to use that capability right? And your eyes were able to see things besides the phone right?" No shit Sherlock, have you never used Facebook and seen…
The legal system is not about truth. It's about corraling 12 fish out of water to your way of seeing things. Throw the judges/lawyers a curveball with something like jury nullification and see how quick things get nasty.