You're right to point out that, in certain situations, recurring complaints are the ones that do the most good for an organization.
For example, at the City of Montreal, we sometimes see that the same issue gives rise to multiple complaints and we notice a trend. We then expand the scope of our investigation and get in touch with the organization, in this case a neighbourhood service, to talk to its expert staff and see what's wrong.
In most systemic investigations, we make recommendations regarding deeply ingrained practices in the system, including logistics and internal issues. These practices lead to people experiencing the same situation over and over again.
In some systemic investigations, we observed situations that hadn't been identified by the complainants but that, as the investigation unfolded, appeared to pose a problem. We issued a notice of concern to the City of Montreal.
That's why any ombud worth their salt must be able to carry out systemic investigations.