Good for him. When the response to trying to protect the project and reduce harassment is... harassment and outlets insisting that they are shitting all over open source and continuing the false narrative that code was stolen? Fuck 'em. They don't deserve the emulator and we don't deserve it for letting them be the minimally opposed voices.
If you are not a copyright holder, then you are not in a position to make any demands. I find it especially ironic, considering when the GPL was actually violated on multiple occasions, even as recently as a few months ago, nobody ever takes issue with that.
Ironic that he says he understands licensing but doesn’t understand that, if you’re not a copyright holder, you don’t have standing to do anything about those violations. The Violations of GNU Licenses page states that if you see a violation, you should confirm the violation, collect as many details as you can, and then:
Once you have collected the details, you should send a precise report to the copyright holders of the packages that are being wrongly distributed. The GNU licenses are copyright licenses; free licenses in general are based on copyright. In most countries only the copyright holders are legally empowered to act against violations.
I remember reading about someone attempting to challenge that by suing for the rights that should have been conveyed to them by the infringer respecting copyright, but I wasn’t able to find anything on it. I did find references to people who were partial copyright holders being found to not have standing due to not having sufficient ownership to make a claim, though - see the outcome of https://sfconservancy.org/copyleft-compliance/vmware-lawsuit-faq.html
And that't the crux of the issue. Stenzek doesn't actually understand the reality of licensing.
The reality is this - you can't do anything without a lawyer. Laweyrs cost money (pro bono isn't a thing in the copyright world AFAIK, but IANAL).
If he wanted to avoid this, then maybe he should've kept it closed source from the beginning. Chinese sellers on AliExpress couldn't care less about licensing anyway, so that way he'd have at least some protection.
IMO his course of action so far has been wrong.
What he should've done is this:
Cause a stir
Get support from the community
Open up donations for the project (or just himself, since you don't want a repeat of Yuzu)
He could even go after Arcade1up legally if he raised funds, but that's not even worth the time if you ask me.
Even if he shuts down the emulator, the code is out there forever. He will be playing whackamole with forks and various other projects just like Nintendo does. The analogy absolutely works for what's happening.