Horseshit. I have something like 50 domains on a popular retail registrar and every single one of them has an MX record, despite me never doing a single thing other than claiming the name; they come by default with new domains. If I was in the Netherlands, every one of them would have DNSSEC signatures too, because European registrars opt domains into DNSSEC by default.

I'm having a hard time articulating how silly it is to try to dunk on MTA-STS for being "vulnerable" to downgrade attacks; it's like trying to say that HSTS is vulnerable to SSL-stripping attacks. You have to not understand the idea behind the attack or the countermeasure to lead with that argument.