A SS X roll has a probability of 7/216 which over 40 PA's a game works out to about the 1.3 that was simmed.
What people don't realize is that the impact of poor defense is exponential. For every X roll that is missed, that out now has to be replaced. So lets say player 1 misses 10 X rolls (errors/singles doesn't matter much at SS) over player 2 during the season.
Not only has player 1 allowed 10 additional players on base due to errors, the team must now replace 10 more outs. If an average team has an OBP of .333, then you actually have to face another 15 batters to make those additional 10 outs. So in addition, to the 10 players you let on base due to errors another 5 are going to get walks or hits, while your team gets the required outs to finish a game.
From a value standpoint, if a hitter averages 700 PA's only 350 of those are coming from his card. So a SS that gets 180 X chances has about a 2:1 offense to defense contribution.
When you compare that to other positions the ratio can be closer to 5:1, so a fair amount of value is tied up in defense for a SS, plus their card is involved in more plays than any other position.
The nice thing about good defense in the mystery game is it reduces the risk of the card since there is no mystery for good defense. So in the case of Metzger, who has no offense you know probably 90% of his salary is tied up in defense. You have effectively removed the mystery out of the game when you use Metzger.