Perhaps some people think we shouldn't use metrics for defense, but I'm not one of them. I am perfectly willing to use defensive metrics, I consider them directionally relatively accurate and useful, especially in your extreme example of Hosmer being better than Fielder. But even the ambiguous eye test could probably catch that one! My point, in the broader discussion of WAR, is how it is converted into "runs" and how that is combined with offensive (and to a lesser extent running) numbers into one number. And I especially don't buy the values of replacement level value of players on the low end of the defensive spectrum and how that inflates WAR value of the better defenders of the best defenders.