It's an interesting take, and you may as well map it to industrial projects, architecture, software to see it from a different perspective.

The timetable is the specs. The product is what your customers experience.

The specs (loose or... very specific) is definitely a major product step. But in that it is a mean to deliver the service/experience in the end. Without the implementation details (that do not live in the spec), you get often unsatisfied people everywhere.