As a Systems Engineer by profession, I mostly agree with Sergio and see project management and process management both as types of systems and both in many ways share primary characteristics with distributed computing where people are the processing nodes and communication channels are the "edges" where the information flows between nodes.
Business management processes define the rule of engagement for project management, so well thought out processes enable efficient workflow. When assigned to process management projects as a PM, I consider the processes like any other product where the goal is to efficiently process inputs to create the desired outputs.
Many product oriented PMs however loathe process management. They want to focus on how the product functions, rather than the business architecture that enables making the products. For me it is a very lucrative technical niche where my job is to balance efficiency performing technical functions like engineering and manufacturing, with business functions like change management and financial accounting/reporting. Rather than responding to KPIs for indications of health, My role becomes defining measurable qualities that provide the insight to make well informed decisions. You could say that Disciplined Agile is my bread and butter because I define the ways of working for specific project contexts.