Doublade has high Defense and is weak to Special moves and CAN be OHKO by a STAB Fire Blast.
Eviolite will boost defenses by 50% and if you plan to run a 252 Sp.Def, it would give you 216 + 50% = 324 Sp.Def, not bad, while Aegislash (Shield Form) can give you a 359-438 in Defense and Sp.Def and having more Attack and King's Shield move.
If you want a Wall/Annoyer, you should use Swords Dance + Shadow Sneak Combo (More a Sweeper) or Toxic maybe (Who uses that)? Rest + Sleep Talk Combo not always works like you want.
Gyro Ball makes great damage and has more power than Shadow Sneak (both STAB).
Also Sleep Talk put all priority to 0 so your Shadow Sneak while using Sleep Talk, will depend on your Doublade's speed..
If you want to use Gyro Ball, use the Sassy Nature which drops speed and raises special defense.
Here is a good set for each one:
252 Atk / 252 Sp.Def / 4 HP or Def
- Swords Dance / Toxic / Shadow Sneak
- Gyro Ball
- Sleep Talk
Aegislash is banned from OU.
Shield Form use King's Shield, if he goes for a physical attack it will lower the Attack by 2 and them you save for a free Swords Dance and If he stays (same SD turn) and makes another physical move and that is super-effective, it won't do almost nothing and Weakness Policy will activate and give you 1.5x in a total of 2.5x.
Shadow Sneak is priority to cover from Aegislash's speed and with 2.5x + STAB it will almost OHKO everything.
Gyro Ball for the slowness and a annoying Xerneas.
Sacred Swords for pokémons with Cosmic Power and etc..
Another thing for Aegislash, if you use Shadow Sneak and the other Pokémon survive, you can be easly OHKO by almost any move, so be careful.. you should have some other walls for resist the weaks of a steel and ghost types.
Aegislash @Weakness Policy
252 Atk / 128 Def / 128 Sp.Def
- King's Shield
- Swords Dance
- Shadow Sneak
- Gyro Ball / Sacred Sword
Defensive talking - The Maximum Defense stat for Doublade with Eviolite is 657and the Maximum Defense stat for Aegislash is 438, but Aegislash has more Sp.Def, even with Doublade holding a Eviolite.
Attacking Talking - Aegislash is better. Shield Form can be useful for use Swords Dance and King's Shield move says all. Aegislash (Attack Form) has more Attack than Doublade.
Hope this helps.