His numbers are hit and miss, but mostly miss. DBRM looked good last year (10th), but were pedestrian at best the years before that. (Typically around 30th among PF.) Defensive rating has been bad throughout his career and got much worse last season. (113 is a sieve, especially for a PF.) His defensive win shares dropped last season pretty seriously as well. Most importantly, RAPTOR and PIPM hate Gordon's D, and the Magic were a much worse defense with him on the floor last season than with him off (109.7 - 105.9).
Part of that may be a change in philosophy or personell-- I'll admit I'm not a big Magic watcher and making Gordon play with Vucevic more often instead of one of the 10 0r 15 long-limbed 8-footers the Magic collect like baseball cards might flavor those numbers a bit unfairly. Part of it may well be noise. Perhaps defensive metrics are too much in their infancy to argue with as well.