Um...
They all look like some buddhist figure but seriously, I believe his G4 comes close to Sun Wukong as his G4 resembles those animals in Rusukaina. Sun Wukong is an incredible shapeshifter. Luffy is the god's enemy, similar to Sun Wukong opposing Buddha.
Also, Luffy is not going to defeat Kaido with his allrounder form. He needs a G4 mode which packs more power.