I'll try to answer that the best I can from my limited knowledge.
I think an ombudsman reporting to the minister has other avenues if the minister doesn't agree with the ombudsman's direction. I think we've seen that with the DND ombudsman where you can go public. I think that's why maybe it would be better to have a legislated ombudsman who can report to the minister, versus a mandated one, but I'm not an expert in that field.