In a land where few pitchers succeed, the consistent dominance of Brad Ziegler is positively tantalizing. Since Ziegler’s first full season with the D-backs, Ziegler has managed a 2.52 ERA, 20th among the 160 relievers with at least 150 innings in that span, and second to just Josh Collmenter on the team. But ERA is ill-equipped to measure the value …