On my small system I feel pretty much the way you do, but large systems have different issues. Someone will get a plausible sender to send them a message with spammy contents, then they will resend that message unaltered to a zillion recipients at large mail systems which is hard to detect quickly since the DKIM, DMARC et al. are all OK. Being able to see there is an extra hop or two in the path that doesn't look like a mailing list is useful for them.
and 30+ years of email content and protocol hacking driven by that view has worked sooooo well
I go to a lot of meetings with people who run large mail systems, but I don't think I've ever seen you at one.
If you have some key insight we've all missed, and that will work at scale for mail systems with billions of users, let me know and I'll pass it along.
just wow! and whose credibility does this ad homina call into question? but back to technology. of the myriad of protection techniques in use by providers large and small, statistically which reject/protect-against how much? actual measures. ip-range filtering, smtp protocol errors & violations, et alia vs dkim, dmarc, even spf. randy