I don't think catchers "vary so significantly defensively". Absent any reason to believe otherwise, I suspect they probably vary about as much as any other position. The other guy was the one taking the rather confusing (to me at least) position that there is almost no variation amongst catchers, and significantly less than at other positions. That's not really what he said. He said the difference between an average catcher and an elite catcher is probably not as large (or impactful) as the difference between an average CF and an elite CF. I tend to agree. I get the hypothesis, I just happen to think it's probably wrong. Here's why. At other spots on the diamond, a guy's defensive rating is mostly a function of speed/range, fielding/hands, and arm strength and accuracy. These are the criteria where one guy differentiates himself from other guys. For a catcher, you can essentially drop speed/range (although the ability to get out from behind the plate to field bunts and chase popups is certainly a factor); the other elements still matter. But you also have to add in a whole slew of other criteria under the umbrella of defense, which have already been discussed. The catcher's job just has many more dimensions to it, and therefore it stands to reason that there is likely more variability in the abilities of the different guys that do it.