Kill Will of the Emperor ofc. I took 3 raid nights to kill Elegon but only half of it to down Will (we killed Ele and had 90 min left on raid time, still managed to six shot Will)
Bring multidotters, they make this fight really easy. Our lock in 475 ish gear did 70k DPS.
Vizier is easier than Elegon but still harder than Will i think. Depends how well your raid dodges discs and how fast you stack under shield (healthstones / personal CD's ftw) Last phase of Vizier is pain, we had three survivors at the end, tank and 2 DPS.
From what I understand, pretty much anything in normal Heart is harder than anything from MV minus Elegon (this is intentional, hence the slight increase in ilvl from the newer 2 raids). So just finish MV and go on from there. Farming only gets easier once you complete it.