Saying that aṣlaḥ is not obligatory upon God does not imply that God lacks wisdom, mercy, or justice. It rejects a specific assertion of rational obligation: a human evaluation of personal benefit cannot simply be imposed as a necessary rule governing divine action.
Affirming divine knowledge, wisdom, power, and justice is a distinct doctrinal question. Those attributes are not established or negated merely by an individual's preference for one imagined scenario.
Example: “This outcome appears more beneficial to me” expresses a limited human evaluation. “God is obliged to produce this outcome” is a further theological thesis requiring its own supporting argument.