Aegislash's lack of speed is key in it's performance to me. after using king's shield, anyone who knows anything about protecting moves is going to know that you are afraid of them, and that they have a free hit on you due to the DOS (decay of succession). the great thing about Aegislash is that after using kings shield, it turns to shield form which raises it's defense. If Aegislash is slower than the opponent, it has a better chance of surviving a hit, then you can use SSneak or SSword. If that attack fails to K.O., you are free to set up another shield. If you are faster and your opponent survives the hit, Aegislash will most likely lose right then and there.
UNRELATED EDIT: 2-1. Close games and annoying tactics were all that that could be seen in this battle. replay's up of course.