You seem to think that a certificate authority is obligated to verify ownership of a domain by email (for DV certs). You are mistaken, and that's not the case. The mechanisms supported by
Let's Encrypt to authenticate domains are
just as good as email verification.
If you've been involved in a CA, then you should be familiar with the CAB forum baseline requirements for Verification Practices. https://cabforum.org/wp-content/uploads/BRv1.2.3.pdf
> For each Fully-Qualified Domain Name listed in a Certificate, the CA SHALL confirm that[] the Applicant[] has control over the FQDN by: [...]
> 4. Communicating with the Domain’s administrator using an email address [...] ‘admin’,
‘administrator’, ‘webmaster’, ‘hostmaster’, or ‘postmaster’ [...] followed by the Domain Name[];
> 6. Having the Applicant demonstrate practical control over the FQDN by making an agreed-upon change to information found on an online Web page identified by a uniform resource identifier containing the FQDN
> 7. Using any other method of confirmation, provided that the CA maintains documented evidence that the method of confirmation establishes that the Applicant is the Domain Name Registrant or has control over the FQDN to at least the same level of assurance as those methods previously described.
The approach used by Let's Encrypt meets this standard (of which email is just one of several options), and the methods they use are just as secure as using email. They specifically offer approach 6. above, which they call Simple HTTP, as well as other approaches that comply with 7. as outlined in https://letsencrypt.github.io/acme-spec/#rfc.section.7 Involving email in the verification process makes certificate provisioning harder to automate and adds no additional security.