Don’t certs just create an ephemeral key pair that disappears after the session anyhow? What does cert validity period have to do with “This is a big upgrade for the security of the TLS ecosystem because it minimizes exposure time during a key compromise event.”
I mean, it’s LE so I’m sure they know what their talking about. But…?
No. Perfect Forward Secrecy (ephemeral keys) prevents this type of replay.