"When Skeletal Shattering procs, Bone Shield provides 24% DR instead of the base 16%. This means that a Skeletal Shattering proc is as if you had a ~9.5% DR cooldown active. In order to calculate the time-averaged value of Skeletal Shattering, the following formula applies:
skeletal_shattering_dr = 1 - ( ((1-critchance)*0.84 + critchance*0.76) / 0.84 )
Example case at 25% crit: 1 - ( ((1-0.25)*0.84 + 0.25*0.76) / 0.84 ) = 0.0238 = 2.38% DR.
A more simple approximation for the DR is that the time-averaged Skeletal Shattering DR is a bit less than your crit% divided by 10, which holds true for most realistic levels of crit. This means that Crit Rating gains about 0.095%, i.e. just under 0.1% DR per 350 rating from Skeletal Shattering." - Thorlefulz
Versatility has two parts - 400 rating gets you 1% more healing and damage done, and it also gets you 0.5% less damage taken you're right that the 0.5% is passive, but that's not why it's good for us that 1% more healing applies to almost everything (doesn't work on bone shield iirc) that we do, including the DS heal and shield so I can spend 233 rating to get 1% more of DS heal as blood shield or I can spend 400 rating to get 1% more DS healing and 1% more blood shield (doesn't double dip, though) and that's ignoring the 0.5% damage reduction.
versatility will affect about 61% of the healing done whereas mastery will affect 27.34% of the healing done, mastery is 1.71 times as efficient as versatility but even with that factored in versatility still does more per point.