"Probably" doesn't cut it. If law enforcement doesn't observe it (as would likely be the case on an E2EE-by-default platform), then there's nothing actionable they can do.
If they do observe it, and the platform owners are responsive to taking down illegal content and/or providing information on the participants, then likely law enforcement is satisfied with that.
you're right. Only they have probably have the fullest data on how much crime is moderated or unmoderated on what messenger, the rest is speculation. He probably just got cocky and overconfident, thinking he can beef with the EU on the same level like Musk or Gates.
If they do observe it, and the platform owners are responsive to taking down illegal content and/or providing information on the participants, then likely law enforcement is satisfied with that.