Wii U VC is confirmed to be way slower than Emulator and DS for IGT purposes since it's IGT does count loading times (~19 minutes). However, it's also being faster than Emulator and DS/(n)3DS in RTA (~10 minutes).

DS/(n)3DS and Emulator are 100% accurate with their IGT, so RTA would just add more inaccuracies to the main platforms. So we decided to keep IGT as main timing. All RTA times get shown nevertheless to be still capable of comparing all times. Runs are also not getting obsoleted if done on different platforms