"Luffy transformed before, so him transforming again proves G5 wasn't an asspull"
Flawless logic
If only it tackled the real issue with G5/Nika Nika, which is its completely out of the blue addition to the story it would be amazing.
Oda sure did a great job shadowing, foreshadowing, and preshadowing it by having the WG not give a rats ass about the fruit or Luffy himself until the moment he was fighting Kaido.