How would you know this? If they access the data from the platforms server you would never know unlike with obvious forceful physical seazure. The point of E2EE is that the weakest link, the server, is removed. It increases the required threat model from simple dragnet surveillance to high effort targeted attacks. If the client is insecure nothing can protect your data and signal has said that many times.

I don't see how the debate about requiring a phone number is relevant to this discussion since telegram does too.