This took A LOT of fiddling and work but I finally have the brightness levels from my different setups close enough for me to consider this project done. Here they all are again side by side.
TOP LEFT: GCN - Composite Cables (Easily the biggest loss of quality and VERY dark.)
TOP RIGHT: Wii - Component Cables using the Wii's Built In Emulator.
BOTTOM LEFT: GCN - Component Cables (BitFunx, Originals are WAY too pricey!)
BOTTOM RIGHT: Wii - Component Cables using Homebrew Nintendont Emulation
I'll have a guide link for this soon. https://www.twitch.tv/kaaboose111