It’s barely anonymous, and poorly encrypted. The latter is the reason Durov is in custody

There is no logic here. If it was poor it would be very easy to track anyone including criminals. You can check the news to find the reasons.

There have absolutely been cases where a backdoor/weakness/lack of encryption used to catch criminals before

I meant telegram related cases.

Some are staying safe, others are being caught precisely because of this.

I didn’t see any proofs of that.

Using better encryption schemes is definitely part of that.

Part of what? I don’t get the point here.