Last time I tried to use Arch for gaming I ran into constant issues like what you describe. Almost like it wasn't using the correct graphics drivers for the games even though I could verify it was. I never could quite figure it out.
If you're not against distro hopping, I suggest switching to Bazzite or Nobara. Plain old Fedora is usually fine too if you're not using an Nvidia GPU or don't mind futzing around with RPMFusion, but the extra utilities and tweaks provided in Nobara and Bazzite are really nice.
Wii U cannot dump GameCube games sadly. I wish it worked too