Small claims court is also an option. This is a hobby site, after all. It’s also a clear cut case. How many takedown notices have they sent? What percentage got kicked back historically? Non-zero? Then they knew they were sending fraudulant claims. If not, they still knew this claim was fraudulent after the site responded and they kept filing takedowns anyway.

Did they address these issues by carefully vetting things they signed under penalty of purgery? Clearly not. The facts speak for themselves. Case closed, I think. I’m not sure you really even need a lawyer (though one would help).