which is still there if you are not using lets encrypt, because they can strongarm them to make a fake cert for your domain, and install a proxy repackaging HTTPS traffic with the fake certificate. all browsers trust the lets encrypt root certificate, so they won't see anything suspicious.

the only thing there today to detect this (but not avoid) is certificate transparency logs. all modern certificates are required to be added to this log, for the CA to remain compliant. but browsers are not checking the logs, that would be a lot of additional traffic and how do they decide if a certificate was created maliciously? also, lets encrypt could afford being noncompliant, browser vendors can't realistically just distrust their root certificate, many sites would become inaccessible.