Many human Mars mission architectures use an Earth return vehicle that is separate from the outbound vessel. The requirements are very different, and there's an overwhelming advantage to placing an Earth return vehicle on the surface ahead of time to produce the methane fuel for its return flight in situ ahead of time, so a vessel that can get astronauts out to Mars without being able to return them is still an important contribution.
On a poignant side note, the article notes that the only feature Dragon now lacks to become qualified for carrying humans is a launch abort system; the original Space Shuttle was designed without a launch abort system.
Many human Mars mission architectures use an Earth return vehicle that is separate from the outbound vessel. The requirements are very different, and there's an overwhelming advantage to placing an Earth return vehicle on the surface ahead of time to produce the methane fuel for its return flight in situ ahead of time, so a vessel that can get astronauts out to Mars without being able to return them is still an important contribution.
On a poignant side note, the article notes that the only feature Dragon now lacks to become qualified for carrying humans is a launch abort system; the original Space Shuttle was designed without a launch abort system.