MoG removes minions from having any purpose throughout much of heroic tier, other than maybe providing flanking for non-minions. The party can effectively ignore an unlimited amount of minions, even if they crit, until they can do more than 5 damage.
If it's an encounter that would actually cause the cleric to use MoG, you still have options:
1) Let the minions use assists to let the BBEGs big hits land easier (You should be doing this even without MoG...it's probably the most useful thing they can do a lot of times.
2) Give your BBEG an aura that boosts minion's damage
3) Use minions for encounters leading up to the boss fight where they'll do their 5 damage, and use a mix of brutes and minions in the boss fight (see option 1).
MoG is fine as is.