You can solve the problem of low software quality via your non functional requirements and setting quality requirements in your team.
When you combine your User Stories with your non functional requierements, the team assures that the software that is beeing build keeps its standarts of quality.

"in real world, the primary advantage' ofagile software dev' methodologies is convenient for `micro-management', which is mainly employed by a business expecting lowcost-running"

Absolutely not. In a agile environment you are avoiding micromanagement by letting the team manage itself. It is responsible for the endproduct and its quality.