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OK...that's a good way to simplify the roof of concept. Let me put it to you this way:
Derek Jeter in 2004 had a UZR of -19 defensive runs at short. The second worst at the position...while contributing 46 runs above replacement. The Cameron approach would say Jeter was worth 27 runs above the replacement level shortstop. That's 2.7 wins. PCA on the other hand...which is a dual-replacement metric, say Jeter was worth 7.6 offensive wins (about 4.5 offensive wins above the .350 replacement level) and 1.6 defensive wins (if you're keeping score, the average shortstop in Jeter's playing time would be worth 2.7 defensive wins, so PCA says Jeter was -11 runs to average so a tad more optimistic)...but even if we took the UZR version as more accurate...that would be 0.8 defensive wins. For a total value of 3.4 + 0.6 or 5.1 WAR (rather than 2.7 WAR).
Let's compare that to a defensive genius like....(drumroll...) ADAM EVERETT.
UZR gave Everett +25 runs/150 games in 2004. Yes...that's a freakin' lot. Unfortunately, Everett is a TERRIBLE hitter. If Everett were a full time hitter, he'd have been worth about 13 runs above the .350 replacement level and 25 runs above average for defense...making Everett worth (um...this is not good guys) 3.8 WAR (!) the Cameron way...whereas PCA would conclude that Everett in full time play was worth something like 1.3 offensive wins and 5.2 defensive wins (6.5 WAR)
OK...now what makes more sense...Jeter being 70% of the player that Everett is in 2004 or 85% of the player that Everett was?
I can hear Doc saying "nay varily...the right answer is...NEITHER"...but I was granting the .350 replacement level. PCA doesn't use the .350 replacement level because that's not how you define real value. The correct way is at the .250 replacement level or lower for offense.
Watch what happens:
Jeter is worth 8.4 wins accepting UZR's evaluation and PCA's offensive margin
Everett is worth 7.6 wins using the same assumptions.
Now what makes more sense?
This is the rational approach, not only because the answers look more logical, but because the defensive margin is DEFINITELY NOT .500 in the real world...and that's REAL VALUE that we need to consider...the REAL DIFFERNCE between a player and thr ACTUAL MARGIN...that's what matters...not what some amalgum replacement player would do. The defensive margin should be higher than the batting margin (because fielding is only 40% of team defense, whichi means the range of performance will be less than the range of team runs allowed...and team runs allowed is the stat that has the .250 margin)...but they BOTH need to be WAAAYYY lower than is commonly applied to roster decision making.
When you do the math in a way that is consistent with the real value players produce...you get answers that make a world more sense.