This isn't about copyright, it's about whether the software's purpose is to break DRM. Ninty argued that Yuzu's primary purpose is to enable copyright infringement which is forbidden under the DMCA; both infringement of course but also even just building tools to enable it. The latter is the critical (and IMHO insane) part.

Now, all of that is obviously BS but Ninty SLAPPed Yuzu to death, so it doesn't matter what's just or unjust; they win. God bless corporate America.