nothing to doubt about whether ER is working or not -> check the numbers, its a sample out out of even more samples which all tell the same story: there is not a single combo under the buffed section which hit for less than the highest number of the unbuffed section; quite the contrary: the buffed combos are averagly hitting for ~400-500 more than the unbuffed(add debuffs and crits to that calculation and you'll see even bigger differences!).
ER works as well on normal white hits, combostarters and even on dots as long as the buff remains un-triggered. hell, you can even preload ER to buff your next white hit and the corresponding finisher if timed correctly. ER is possibly the best tier2 feat next to retaliation in this game
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rune of grounding is a must for zerk-situations. doesnt only work against direct caster damage but also vs several sind and dt proccs, bomb, pets, dots etc.
dont take the bs as a lonesome whatever, do as much as possible to support your team and youll turn the tides of minis -> thus if you find rune useless in 1o1 bs vs running caster situations, you dont see the whole picture