Hit Rating and Expertise

[Dem]

Relying completely on maths limits your tanking because maths cannot adequately model tanking, just single and simple aspects of it.

In Ulduar we couldn't intelligently use CDs as we were fine then we were dead. Now it's different. We have plenty of cool downs and the time to use them when required. The correct use of CDs is far more important than another couple of percent block.

Having a predictable source of self healing is effectively another type of CD and appears to be underestimated currently.

The answer is simple, gear to your raid and the encounter. Use the available research but be consider how it relates to your situation.