What is the misuse here? The DMCA makes it illegal to distribute software whose intention is to circumvent technical measures that prevent access to copyrighted materials [1]. youtube-dl's own documentation provides instructions on downloading copyrighted music videos and its test suite uses copyrighted material as well. It's pretty hard, although not impossible, to claim that the intention of the software isn't to engage in copyright violations given those two facts.

Okay so you make a counterargument that maybe this qualifies as fair-use or falls under some other exemption. Maybe you're right, maybe you're not right, that's for a court to decide. The RIAA's lawyer is not here to defend youtube-dl's position on the matter, youtube-dl has the responsibility of defending itself and demonstrating why it chose to use copyrighted music videos as the key example and use case.

You can object to the law and you can even provide a defense for youtube-dl and counter the takedown notice, but you can't say that RIAA's lawyer abused the DMCA takedown process by defending its client.

[1] https://www.copyright.gov/policy/1201/#:~:text=Enacted%20in%...