Ah, the joys of putting a roster together with your best players. Tanney might very well not be even Matt-Moore quality. And he doesn't deserve the roster spot if he doesn't continue his strong preseason play.
That said, you put a QB who might be Matt Moore on your roster, every time, if you can. You do it because you don't know what his ceiling is actually going to be. You do it because a career backup QB is more valuable in terms of cap space alone than a 7th LP or 6th WR or 4th RB. You do it because, if you think you have the right guy, you save yourself a higher pick on a developmental QB in next year's draft. You do it because teams would have traded mid-round draft picks for a player like Matt Moore had Dallas continued to develop him and played him sparingly in preseason and he played well.
Most of all, you do it because the other players you'd keep on the roster instead all very likely *will* make it to the PS. If they didn't, you'd be able to replace them with a street veteran FA they way we did last season with Frampton, or Poppinga, or Armstrong.
Alex Tanney doesn't hurt your team's depth all that much being on the roster, since you're not bringing all 53 to the games, anyway. He ends up being one of the guys who you don't dress every week, so you just have one less player to choose from for your game day roster. But every team is leaving guys off the game day rosters. One of yours just happens to be a QB.
As to the strong and the swift winning races and fights, I agree. Keeping the most valuable resources on your roster is what a strong team does. Tanney hasn't proven yet that he's valuable enough to deserve a spot on the 53, but he's got one game left to do it. If he plays well, he'll make this team, and we'll have to endeavor to persevere without the Caleb McSurdys or Jeff Heaths or Phillip Tanners of the world. Somehow, I think we'll manage.