I can see where the GP is coming from. I suppose it depends on your definition of productive -- there are lots of things in life that can produce feelings of accomplishment and satisfaction even if you don't make any money at them (playing music, studying martial arts, hobby coding, etc). I personally classify those as "productive" activities.
Gaming can be a good way to relax or kill time if you're bored, but in the long run I don't find it as rewarding as my other hobbies. On the other hand, if I'm a bit tired/unmotivated, and have a good game at hand, it's easy to spend all day playing it. But at the end of the day I'll be less happy than if I did something "productive".