While I think there are certainly plenty of Rosharans that view the Listeners as subhuman (calling them savages, for instance), I don't think the Stormfather was implying anything like that in the quote you mention. Listeners obviously do have intelligence, free will, and choice as shown by their interactions with the Stormfather when they go out into the storms to change forms. "Subspren" are things like ordinary windspren. To say Syl is a step above them is not hateful, it's a fact. They only act on instinct (as far as we've seen), while she is capable of thought.