Well, a few things:
1) Muyingwa uses AoE melee attacks, and thus is not affected by Slow. - SE has said they are going to change this, but they have not yet AFAIK. So there's no reason to Elegy it.
2) Muyingwa is wind element, and thus is strong against earth. You're probably fighting a losing battle trying to Elegy it.


Here is a post that discusses current MAcc sets:
http://www.ffxiah.com/forum/topic/35...to/16/#2612927

Here is my current debuff set, which works pretty well for me against all content (but isn't reasonable): http://www.ffxiah.com/item-sets/323292
Bokwus Boots are MAcc path and Genbu's has MAcc+5 augment.