I like how you're citing endgame bosses and Mercy Stroke, without observing that Mercy Stroke can be used a half dozen times in T5 and T4 (nevermind T2), particularly on strict add DPS checks like conflags.

Bottom line: replace Bloodbath or Fracture with Mantra, not Mercy Stroke. Bloodbath is only relevant on T4 when AOE'ing adds, or for long, sustained damage intake like bigADS on T2.