[tastroder]

Maybe the data model is used for two use cases, one where you primarily access owner entities and one where you primarily access invoices and occasionally do something with their owner. Just because it does not fit some weird, hypothetical prototypical API it's not inherently "bad design". APIs aren't ER models, sure, they're supposed to make sense but they're also supposed to help their consumers perform a task.

And let's not kid ourselves, much of our world runs on APIs that would really deserve the "bad design" handwave, end of the day that's often an aesthetic question.