Okay a little update, I found a program called F3 for Linux and Mac. It fills up the entire drive with data and then checks if the data is unmodified. It took a while to write 128GB with 17MB transfer speed

. Verifying the data now and everything after the first 20GB is 100% corrupted. Soooo it's most likely the corrupted SD card if anyone finds this post in the future. Maybe the Wii checks for corrupt SD cards and won't boot if one is inserted?
EDIT: All the files after 28GB mark are 100% corrupted