Protecting end users from nothing at all (like I said, there is no offending URL) is not more important than making sure Google doesn't literally gatekeep the entire Internet, IMO.
As an aside, your commentary about Google alerting to phishing emails seems like you're misunderstanding and trying to use this to further your "it's all random!" claims. They aren't flagging it because of the sender, but instead because the contents included a URL on the blacklist. Google re-scans and when they find URLs that are now blacklisted, they warn about Phishing. This isn't new and they've done it for years, and it seems pretty obvious and logical.
e.g. "That email you got a while back that claimed it's from the Netflix billing problem website is actually phishing. If you gave them details, that's a problem".
"Protecting end users from nothing at all (like I said, there is no offending URL) is not more important than making sure Google doesn't literally gatekeep the entire Internet"
This system protects countless people from malware and phishing daily. I have no reason to believe your particular claims about this (though I'm skeptical given that you are blocking details that would allow others -- such as Google -- to repudiate your claims. Why block the subdomain? If it hosts static resources, what's the concern?).
But of course, they don't flag google.com as a spammy domain and stop all emails coming from it, right?
PS: Im not sure exactly what you are disputing. Are you suggesting their report pointed to a smoking gun on my site, and I'm lying? My experience is not unique. There are plenty of instances of the same type of issue affecting other people in the very comments you are reading.
It detects blacklisted URLs in emails and sends warnings, retroactively given that sites are caught some indeterminate time after they might have been communicated (flagging if you have interacted with the email and thus might have been compromised). It seems like it was perfectly reliable.
That isn't damning at all, and it should embarrass you that you cited that, seemingly confused about the reason.
"Im not sure exactly what you are disputing"
I'm saying that we have zero reason to believe you (but reasons to not believe you given that you're redacting things that don't need to be redacted). People caught in the nets of things like this -- through their malice, carelessness, incompetence, etc -- always claim innocence.
For what it's worth, it's all true :) Good luck to you.