A product developed in an Agile process still has a 'maintenance phase'; the idea of software maintenance is not a Waterfall concept, it's a Software Development concept.
One thing I think you're having trouble with (maybe) is that this article was about Scrum, but you're attacking Agile. Scrum is an implementation of Agile, or maybe better characterized as a process facilitating Agile development, but it is not uniquely Agile. There are other Agile implementations/processes (Kanban, XP, etc.). Agile is more about attitude than implementation.
What Scrum is attempting to do is break down big ideas into small workable units, and help teams organize, assign, track and complete those work units efficiently. It separates the development cycle into several sprints: a team works a selected amount of items per sprint based on their capacity vs. the 'weight' of those items. If the development process using Scrum incorporates accepting changes to requirements or the design along the way, it's Agile. If it doesn't, Scrum can look a lot like a series of tiny waterfalls; you can absolutely have a Waterfall process where your teams organize and execute work like Scrum.
The most important thing to keep in mind is that neither Agile nor Scrum dictate what you consider to be a finished product, or a successful product. The standard of quality you added to one of your earlier comments is absolutely achievable using Scrum or another Agile process - in fact, it is the stated goal of Agile to turn out a high quality product which meets stated requirements.