Surely one of the main points of the exercise was that, precisely because there wasn't a curve, whole-class cooperation can result in everyone in the class gett

Surely one of the main points of the exercise was that, precisely because there wasn't a curve, whole-class cooperation can result in everyone in the class getting a higher score (20% higher) than they usually would. Grading on a curve wouldn't be the same game just 'more interesting', it'd be a completely different game, and one that's lost most of the "To win at some games, cooperation is better than competition" aspect.