There are instances when pure statistical analysis is necessary. There are instances when no statistical analysis is necssary. However, both of the above instances are extremely rare. There generally has to be a comingling of statistical and perceptual data, and judging defense is certainly one of those cases. Defensive metrics (or those defensive metrics that the general public know about) are laregly much more flawed than offensive and pitchers metrics for the simple fact that defense is much more of a reactive statistic while pitching and hitting are proactive statistics. A batter can choose to swing or not, a pitcher (to some extent) can choose whether or not to throw a strike (or, try to make the batter make contact; at the very least, you could say the pitcher controls the ball) - there is no situation in which a pitcher and the batter are not involved in every play (save for pick-off attempts or balks or similar on-mound events). However, defense, much less individual defensive players themselves, are not involved in every play. This makes defensive counting-based statistics almost irrelevant, especially when comparing players on different teams. Even comparing players playing the same position on the same team becomes problematic because of small sample size - if a guy gets 5 balls hit his way per game, and 2 or 3 guys divvy up the games during the year, there just probably aren't as many chances to go around as might be necessary to form a valid conclusion. I'm sure there are very good defensive metrics out there (mainly those based on computer-measured range), but I'm even more sure that we simply don't know about them because clubs won't give up their proprietary information. Why would they. So we're left with defensive computations that put players on different teams at great advantages and disadvantages to each other. So, I'd say that without these good defensive metrics at our disposal, what we observe on the field in terms of range, throwing arm, etc., is at least equally as important as to what we read in the statistical tables. Some inferences can be made with defensive statistics, but they are always mitigated by the weakness of their own composition.