You're actually right on the mark. Of course Tlacaelel, the architect of the Mexica Triple Alliance, had instilled into the Aztec leadership the thought that they were a distinct, chosen people, the sons and daughters of the Left Handed Hummingbird, and that by this, they had the right to dominance over people who weren't that much different from them.
Interesting.
Sounds like a fairly stable situation as long as the Aztecs are capable of being top dogs - meaning, as long as they're the strongest in the area, they can get away with this. Once they're not, someone will try to take that position.
But not so much resentment of being their subjects as wanting to be the ones collecting tribute instead.