The simple answer is that a DH has negative value to a team if he is only a DH. I have never liked any of the advanced defensive metrics or WAR based inflation by position. I get the argument, I don't buy it. If you want to say SS is the most valuable position, fine, but you still need 8 others, and not every ball is going to be hit there. Obviously, not everyone can play SS. Nonetheless, the position (not the player) is one of eight and a ****** defensive SS (the player, not the position) shouldn't be inherently more valuable than a good defensive 1st baseman who can dig out bad throws from the ****** SS.