The claim isn't that robots have no use or that humans are better for exploration. Strictly speaking it only claims that there is some exploration that only humans can do well.
Yes, we could get lots of science done fairly quickly by putting a couple of people on Mars for a few months. However, it still comes down to that for the resources it would take to do that, we could put hundreds of robots on Mars that could work for years, each doing their own little specialized job, and do more science and get the results sooner.
I hope we do send men to Mars but I seriously think people do not realize how much that will actually take to do and how long it will take. The ISS is the most expensive project mankind has worked on and it hasn't even left orbit. It's resupply missions don't have to leave orbit. It doesn't have to deal with deep space radiation. It doesn't have to support it's own independent landing and launch facilities. etc. etc. etc.