what happens if second half of Alex is all physical?

[Brian_]

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.

Except when you actually try to push your performance, you don't use your CDs like this.

Even if you're being conservative with your CDs, you SS+SW+DA DM first, SS+DA DM the second, and SS+SW+DA DM the last. And, you're also going to have Delirium up for 10% reduced damage and maybe Reprisal. Your mitigation is much better than a PLD. And, you retain Living Dead as an emergency button while PLD actually has to use it in their rotation.

But let's be real. Unless your healers are bad or you're all undergeared, you don't have to do that. As a DRK, you should DA DM + SW the first, Living Dead the second, DA DM + SW the last with Delirium and maybe Reprisal up for the first and last. Still more than enough to survive the hits. It lets you use your SS purely to reduce the general incoming damage. Between SS and Conva, you can negate the mitigation loss from dropping Grit and tank all of the fight while pure DPSing and further increase the gap between DRK and PLD DPS.

On the otherhand, the PLD is stuck on a very inflexible CD rotation and only has 1 free Rampart after the split to help reduce general damage while DPSing. The result is a squishier tank that has less DPS.