Why does it matter what the reason is for the end user's preference? Or if the data is being stored in a way that's currently difficult to deobfuscate? It's ironic that the whole push is "end user privacy", ie something that benefits the end user, but multiple workarounds are offered when the end user (for whatever reason) doesn't want their visits logged on a third party.
As long as none of your personal data is involved, it's not your data. It belongs to the website operator, and they can do with it what they please.
I don't know how else an end user can express their preference.
IP addresses are PII under the GDPR with enough context - although honestly I don't want to go down that horrible rabbit hole.
But sure, sure, the site operators can do whatever they please. It's just Plausible banging on about being privacy friendly and ethical seems a bit ironic and is frustrating to see.
Edit: The DNT flag is explicitly ignored by Plausible as well: https://github.com/plausible/analytics/discussions/646
You're really stretching definitions here, and have yet to make an actual argument about how Plausible invades your privacy. I'll just end my involvement in this discussion here, because it's clear to me that it will not be productive.