This is an interesting application of the American system and laws. What you're generally presenting are two tiers of rules.

The difference between plagiarism in art and ripoff as you have presented is roughly the same as the difference between plagiarism in text and spinning. The first is a direct copy, the second is a modification based on the original. This is understood and is a good parallel.

The biggest obstacle in general here is user education. All users are asked to do is give credit to wherever the original source came from. The reason many don't is they're afraid they won't be curated. This is untrue but this untruth has been thoroughly spread through the Discords and through the community. It is likely it's been perpetuated by some curation projects that are no longer active, but it still instills fear among the userbase. Obviously you know as well as I do it's complete BS and a decent curator will still value someone's work even if they properly reference everything.

A secondary issue is cases where a user has reproduced something by a currently active artist who is exhibiting and selling their work. I've had artists in full hysterics because someone replicated something of theirs and now it's showing up due to the strong SEO overtop of their own work. When they sign up for exhibitions or galleries, they're treated as the plagiarist. So all because someone didn't cite a source, the artist loses his or her income. You're probably aware how significant a high-end gallery spot is to an artist that's struggling to get by.

An overarching issue we're facing is highly-organized rings of thematic account scammers that look for every loophole to exploit and develop accounts to resemble genuine users. They typically target the art community because of higher curation; the work they put into their endeavors is minimal as it's an assembly-line type approach. Over the years we've and the anti-abuse community in general has dismantled quite a few of these, although handling them is both difficult and dangerous. Targeted harassment the likes of which most users, even during whatever flag war, have never seen is common when dealing with the most severe of these. Death threats, social engineering, hacking, and everything else under the sun has occurred in relation to these.

Right now I'm personally working on developing guidelines that would clarify the distinction between the above and the more common art hobbyist who, while presenting unsourced art, is not an organized malicious actor.