They don't need Signal to do any of this though, so this doesn't seem like a very plausible theory.

Seems like a lot of unnecessary steps there

What are you doing to help others escape WhatsApp, anti-libre software?

This is what the UK police do with WhatsApp data. Even though they can't read the messages, they do use the connections of messages to suspicious characters as evidence including date and times, which also puts these other people in the spotlight, opening further investigations.

The UK police can also use 'stinger' devices that are "fake" mobile data towers to intercept mobile communications.

Your theory sounds legit