We have investigated this unintended information disclosure and have concluded it's the fault of the users for having information.

It does if you consider it from the point of view of a. Someone went out of their way to design this API so as to allow this or b. A team of individuals deployed it without realizing how it would be exploited

You can generally learn things from a breach, but finding and remediating systemic issues like those mentioned above is a big ask

Edit: I either responded to the wrong comment or misunderstood what you said. It's late in the day...