Consider Philae - if it had landed a few meters in another direction it would still be working. If it had been a manned expedition, that wouldn't have been an issue.
For the cost of getting humans to and from an asteroid on a decade long mission (in anything approaching a functional state) we could have sent thousands of unmanned landers. Sending people adds a gigantic cost premium. It's nonsense to suggest the rover mission would have been better with people, it wouldn't have happened with people due to cost, and if we could afford the cost of sending people we could do hundreds of unmanned missions for the same cost as one manned one.