What do you mean it's "meant" to be played in co-op? How do you know? Where does it say?
other than what Multidirectional said, they were advertised as such rather explicitly. it's probably still mentioned somewhere in the DLCs blurb on steam or bamco pages or somewhere official. but yeah, all 3 of the challenge areas are just lazily designed bullshit. they seem to be inversely proportional in quality to the main areas
