Henrik Kniberg is one of my favourite Scrum and Agile gurus. His work helped me to implement Scrum and Kanban in different companies. He has a simple but wonderful video on what a PO does and why we do need one. Check it out.
No one knows where the top is, the moment when you have mastered agile. It's a never ending journey, just try getting better and better at it. Take a look at this wonderful example, of the greatest Sushi chef in the world.
In 2001 a bunch of well to do software developers got together at a Ski lodge to discuss a better way to develop software. The outcome is the Agile Manifesto, a constitution for a new way to build software. What followed was the Agile movement.