Looks like you have not yet experienced what a real Product Owner is? The PO is the one guy OWNING the WHOLE product, i.e. banking services, or the webshop, or whatever. The single neck to wring by the CEO if the PO does not deliver proper ROI. Not some clerk who owns a list of requirements.
In businesses that have matured business agility, HR is agile too, so you would be promoted for showing learning abilities, agile mindset, development, etc, but not on being good in a single skill. This is because single skilled people are not so valuable for these kind of companies.
the team, so team members together need to be able to ship DONE. This requires domain expertise in the team. Which team member that is and what their “non-scrum” title would be is irrelevant. Note that the idea of defining is challenging. Introducing a leader role in the team deprives other team members from learning and taking on responsibilities.