Why did Quetzalcóatl and Tezcatlipoca dominate the Aztec creation story?

Thanks for your kind comments and fine questions. Here we won’t be able to answer all your points, but we’ll have a stab at tackling the main one, regarding the roles of Q and T in the Mexica creation story. Xipe Totec was also known as the Red Tezcatlipoca - the supreme creator couple Ometeotl gave birth to four sons (Red T, Black T, Q and Huitzilopochtli). It was the Black T and Q who, as you say, dominated the creation myth. In fact all four brothers were responsible for making fire, heavens, earth, sea, underworld, first human couple, and the sacred calendar. But (Black) T and Q played the most important role of creating heavens and earth. Yes they competed against each other, but they also (later, in restoring heavens and earth, when they dismembered the great earth monster Tlaltecuhtli) collaborated as allies. This reflects what Karl Taube sees as being at the heart of Aztec ideas of creation - ‘the interaction and exchange between opposites constitute a creative act’. T and Q figure prominently in the story of the four previous ‘suns’ or world eras, ‘as if the multiple creations and destructions are the result of cosmic battle between these two great adversaries’.

Quetzalcóatl (L) and Tezcatlipoca (R); illustrations by Miguel Covarrubias