Nietzsche referred to a "master morality" and a "slave morality" in his works, and although his perspective is quite different from (and even opposed to) that of both Hiram and Ta-Nehisi Coates, the distinction he draws is highly relevant to the differing moral attitudes in The Water Dancer. The Quality, like Nietzsche's masters, are arrogant and violent toward the Tasked, who are more conventionally virtuous than their masters, in their compassion and brotherhood.
The moral perspective of the Quality is suggested in their collective name. They view themselves as being intrinsically superior to the Tasked, to the extent that they do not view the Tasked as fully human. This idea, according to Hiram, places a strange and corrupting moral burden upon them. They must become ever more arrogant, brutal, and inhumane, since if they were ever to admit that they are exploiting their fellow humans in an unconscionable manner, they would lose their claim to be considered high in "Quality." No such hypocrisy is demanded of the Tasked, meaning their lives, though terribly hard, are not corrupt and corrupting. Coates shows how the actions of the Quality make them morally inferior to the Tasked, since morality involves both decency and honesty.
Corinne is an interesting case, since she is one of the wealthiest and most privileged of the Quality, yet she is secretly on the side of the Tasked. However, as Hiram points out to her, she retains the autocratic haughtiness of the Quality in her attitudes and her insistence on control. Even one of the Quality so completely reformed as Corinne in terms of morality cannot quite divest herself of their characteristic arrogance.