IANAL either, but the RIAA letter never claimed to be a valid DMCA 512 takedown letter. It simply listed a series of facts, beliefs, opinions, and requests, none of which seem fraudulent, as far as my lay reading goes.
If someone sends you a letter saying:
"Dear qw3rty01: You're hosting Python. Python can be used to circumvent my copy protection provisions. I believe this is illegal under 17 USC §§1201(a)(2) and 1201(b)(1). I ask that you immediately take down and disable access to Python."
They're allowed to do that.
So long as they have a genuine belief that Python violates §§1201(a)(2) and 1201(b)(1), they've sent a stupid letter, not an illegal one. I believe your only recourse is to ignore it.
Your understanding of legal fees is incorrect:
1) I don't need a countersuit to recover legal fees. I can generally file a motion in the original litigation.
2) The US doesn't have federal anti-SLAPP laws. Some states have anti-SLAPP, but even there, there are open legal questions on how state laws interact with federal law suits. Unless you happen to live in a state with anti-SLAPP and one where precedent says state anti-SLAPP laws apply to a federal law suit, you're probably out of luck.
3) Even so, anti-SLAPP is designed for specific types of legal intimidation; I'm not sure this would qualify.
I just looked at the RIAA DMCA repo, and the situation is more complex than reported. The RIAA got a court ruling of some sort in Germany. That throws all sorts of wrenches into all sorts of analyses.
