Assuming one considers Dark Dance and Bulwark to be roughly equivalent CDs (consider their relative uptime/duration/recast/potency), and the fact that Dark Dance can, beyond the use of the buff itself, be used to control Reprisal usage, then really the only tool PLD edges DRK out on physically is Sheltron, which barely counts. DRK's physical mitigation is not as pathetic as people make it out to be, its just that Dark Mind is so OP in comparison. But on the flip side, when you consider Sentinels stronger potency, HG, and PLD's ability to SS/Clemency itself, I wouldn't worry if I was a PLD in the face of a magic tank buster. Case in point:

A1S CD rotation:
PLD 1-Rampart+Sentinel (60% mitigation), 2-HG (100% mitigation), 3-Rampart+Sentinel (60% mitigation).
DRK 1-Shadowskin+DA Dark Mind (50% mitigation), 2-Shadow Wall+Shadowskin+DA Dark Mind (80% mitigation), 3-Shadowskin+DA Dark Mind (50% mitigation).

So, you see, PLD really isn't hurting that bad mitigation-wise. Its still edging out DRK in terms of magic mitgation in some cases.