The heal you gain from death strike is increased by your stamina. And then the blood shield you gain is multiplied by your mastery bonus. The more stamina you have, the more you want mastery. And the more mastery you have, the more you want stamina.
another point branching off of pipastrilo would be is there a point when stamina is high enough that it becomes more valuable than mastery just based off the minimum 7% giving a greater bloodshield than what would be granted than someone stacking mastery.