Well, first I would struggle with the idea that the novel needs to be based around social and political criticism in order to be literature worthy of the widespread recognition and praise that Bless Me, Ultima has received. Since when is this a requirement for literature?
But since you are looking for a validation of that criticism, consider the fact that the novel, while dealing specifically and thoroughly with religious and cultural conflicts of American Latinos in the Southwest, does not comment about racism and isolation of the time period the novel is set in, and could be argued that it reinforces some stereotypes about Latinos that could be misinterpreted by non-Latinos when studying this book.
It is not militant or angry as a novel or story. Anaya does not seem to want to make the story into a commentary that has political overtones, and as good as the novel is, as revolutionary it is in terms of literature, there was a good opportunity for him to make more of a statement.
The Christmas play scene in the book is the perfect statement of the religious confusion in the community - the conflict between Catholicism and traditional native beliefs and practices.