Well, when you lose to a fairy because he only has a Dragon Attack...Don't say I didn't warn you. And as said, they're at least forcing a switch, and potentially allowing them to buff.
As said before, you need a mega, and also, if you're only running 4SA on Aegislash, don't run Shadow Ball. 252SA/4Atk is ok, due to priority, but not the other way round.