In my opinion it all comes down to the definition of product quality.

From the Product Manager perspective product quality is defined if the developed/delivered product is the right product for the targeted customers. It is the result of what the development team has built, and the Product Manager is held responsible for that. Therefore, the success of a product is a major factor in defining product quality and is outcome oriented where the delivered product answers the needs of the customers. 

However, from a Product Owner’s perspective product quality is defined by the output the development team has generated and to what extent this output went through quality assurance. It answers the question if the developed/delivered product was developed the right way and therefore is more output oriented.

To summarize both perspectives, product quality is defined by outcome as well as the output. The product must be the right product, done in a right way. To determine a key position or role to allocate responsibility for product quality, the organizational structure must be considered. In most successful cases however, the Product Manager is and should also fulfil the role of Product Owner which is basically a subset of product management responsibilities. All in all, the Product Manager should be held responsible for product quality given the criteria mentioned above.

Reflective questions:

• How does a successful team constellation look like that enables the PM to successfully fulfil the duties and responsibilities of the PO without neglecting any PM tasks?

• In what organizational structure does a PM / PO split make sense?