What proportional recourse do you suggest when Whatsapp are effectively in contempt of court (in absentia)? In most jurisdictions, obstructing the course of justice usually has heavy penalties.

End to end encrypting doesn't magically cause metadata to disappear. IP addresses, the times messages were sent and received are still useful to law enforcement. In this instance, the court want the IP address of the accused so they can follow up with the ISP.

I prefer warrants written out for specific individuals to dragnet surveillance.