This is Ciara from the Content API support team. Thank you for reaching out.
I understand that you'd like to get the diagnostic data of your products. From the Content API's perspective you can use the productstatuses.list. The productstatuses resource is used to view information about the status of your Shopping products. The list method returns all products, regardless of their validity.
Another method is to use our Reporting service, you can use the ProductView table of the Reports service to show a filtered view of your product data, including product statuses. For example, you can query ProductView to list products that have issues, so you can resolve them.
Once you get the information via the API, you will need to post-process the result to be saved as a csv file.
Let me know if this work for you or if you have any questions.