Hi there
For odyn im a bit unsure... but normaly adds or the 2 mini bosses are spawming when you freshly got your 10 stacks.
but 6-7 stacks are atleast better then any other stat stick ( if wearing the nightbane chest ).
for helya its also hard.. phase 1 its good , phase 2 useless.. phase 3 medicore.
for EN:
Ilgynoth: here is EoC realy bad
Elerethe: just tunnel the boss
but for the rest of the en bosses it should be fine, cenarius has some add switchting but i think the time to get the buff to full stacks is worth it.
Problem is that the buff disapear when attacking something else, so the rupture on cenarius while switching to the adds will also deal less damage.