In what ways do the images of De Las Casas differ from the images of the Aztecs?

Bartolome de las Casas was a sixteenth-century Dominican friar, notable for his chronicling of the colonization of the West Indies (and his eventual opposition to the atrocious treatment of its indigenous people).
De las Casas began his chronicling as a fierce advocate for the religious reform of the newly colonized Indians, supporting the rigidly structured institutionalization of the Indians for the sake of spiritual salvation. However, de las Casas quickly grew opposed to his own (and his contemporaries') views & methodologies, and he spent the rest of his life trying to dismantle the inhumane institution of colonization he had initially supported. In his book Apologetic History of the Indies, de las Casas goes so far as to claim the Indians as being more advanced and civilized than the Greeks and Romans, referring to them as "enlightened" and "virtuous" (Chapter CXXVII). De las Casas can be considered one of the earliest proponents of basic human rights, acknowledging the humaneness of the "barbarians" of the West Indies and serving as an advocate for better treatment of them within the confines of colonization.
One can say this greatly contrasts with the general image of the Aztec, who weren't lucky enough to have advocates like de las Casas on their behalf, at the hands of Spanish conquistadors. One of the most notable chroniclers of the Aztec people, Friar Bernardino de Sahagun, however, professes some admiration of the Aztec in his Florentine Codex, writing that they "are held to be barbarians and of very little worth; in truth, however, in matters of culture and refinement, they are a step ahead of other nations that presume to be quite politic."
http://www.columbia.edu/acis/ets/CCREAD/lascasas.htm

https://www.wdl.org/en/item/10096/