Yes, Downey was the savior of the team in 2007/08. Wings had 115 points, 257 Goals For, and Downey scored 0 of those goals. Shew, good thing Downey played those incredible regular season games, because Red Wings would never have scored 257 goals and closed the season with 115 points and made the playoffs without him. Wings would have been the 2010 Oilers if not for Downey's whopping 3 assists that year.
Your ingenious logic is something very.... special. 
I like comedians cause they make me laugh! 
Conversely, was Downey the reason that the Wings didn't have 120 points in 2008? It's fine to argue that he didn't add much offense, but he wasn't the only player not scoring 20+ points. The fourth line isn't supposed to have three 20+ point scorers- that's why they're paid 500k-1m.
I'll paste my last post here again since you seem to be dodging it.
Downey is on a tryout with the Wings. Would it be responsible for the Wings to invite him and then not let him play? That is not how this organization works.
If the Wings carry 14 forwards I think there is a place for him on the team. If the 14th is only going to play ~30 games, would it make sense to have one of our younger prospects sitting out for ~50 games a season? The younger (more skilled) players need playing time to develop. With Draper as the 13th, the 14th will not play (unless there are a lot of injuries) much. In the case of injuries, the young players can be called-up. I think it would be a waste for I. Flip, Mursak, Tatar, etc. to be off the ice for a large amount of time. You could argue that Miller or Ritola are better options than Downey, but I am not sure they would want to be in the press-box that often.