I'm really on the fense about altering the diet. I've used the same feed for chicks and ducklings in the past and never ran into this problem. The two muscovys that have the angel wing are brother and sister. On the female her left wing is affected and on the male both wings are affected.
As with all animals, the exact nutritional needs of every individual vary. Could be that those two simply needed less calories/protein/etc, so the feed made them grow too rapidly whereas everyone else was fine on the same feed. And that's also where the genetic component, if there is one, might come into play. If they had different nutritional needs, they might pass those same needs to their offspring. Or maybe not.
Or maybe they overate and caused the rapid growth that way.
I raised a lot of ducklings on the same feed that the mallard that got angel wing was raised on, and they were all fine. He simply might have had different nutritional needs than all of them, and that's what caused it, or he might have overeaten.
I would say if the feed is working fine for all your other ducks, you probably don't need to switch it.
Here is a very interesting article about angel wing: http://www.metzerfarms.com/AngelWing.cfm