The point of SPF/DKIM/DMARC is to bind emails to domains, so no more spoofing. It is naive to expect authentication alone can reduce spams.
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To be fair, SPF saves mail.ru and outlook.com users from five, maybe six spam emails per month coming from my domain, based on DMARC reports. If those numbers scale to include every domain on the internet, that's a huge amount of spam being filtered out very easily and very early.
You'd think spammers would've learned to avoid SPF domains at the very least but they haven't, so despite SPF/DMARC/DKIM failing to get anyone out the spam folder, the technology is still catching spam bots.