I contacted Apple. The support agent told me multiple people had contacted support about sound quality issues against the same serial number. Apparently a lot of people get these and don't figure out that they're counterfeit... they just call in with issues like "one side of the airpods sound weird".
She did not have a way to report a counterfeit in her system, she had to report it as a miscellaneous issue.
It appears apple is sitting on their hands on this issue, content with letting people learn their lesson.