Re: No, it's not settled
I don't know if I'm giving you too much credit, but you are very much conflating issues here. 1) The security of the people as a whole against bad actors who use e2ee in the commission of their crimes, and 2) the security of the people as a whole as they use e2ee to protect themselves against bad actors wanting to snoop on, or interfere with, their online communications.
To clarify your use of Zimmerman's metaphor, the envelope exists to prevent people from reading the letter who should not. It also servers as a guarantor that the letter really is coming from whom it says.
In particular, MITM attacks on financial transactions rely on strong encryption. With weak encryption, they entire online marketplace (to include online banking) becomes intractable. E2EE is not required for this only because we assume that the people at the ISPs are good actors who have not been compromised in any way. This has always been a dubious assumption, and is becoming moreso with time.
Moreover, if you have strong crypto, then e2ee is straightforward to implement. And it does NOT particularly stand out, because many streams are of already encrypted data. This last move in the US to explicitly allow ISP commercialization of our online activity driving more of this.
Finally, the issue with the key under the doormat is, well, key. If some form of backdoor were implemented, its existence would be known for months or even years before implementation. The details, including the master keys, then become target #1 for every cracking operation on the planet. Most notably foreign intelligence services. Is there ANYONE that would make a bet that the system would remain intact for five years?