Human intention and choice remain meaningful in a voluntary act, but the servant's capacity is not an independent creator. In the position under discussion, both capacity and deed are under God's creation, while the moral attribution of the deed to the person rests on intention and acquisition.
Acknowledging human capacity is different from asserting that the person independently originates the act outside divine creation. The latter does not follow from the former.
Thus, affirming created capacity does not deny choice, while affirming genuine choice does not confer autonomous creative power upon the servant.