Mega Garchomp should look something like either of these:
-Swords Dance
-Outrage/Dragon Claw
-Earthquake
-Stone Edge/Fire Fang
Nature: Jolly
EVs: 4 HP/252 Atk/252 Spe
Item: Garchompite
or
-Earthquake
-Draco Meteor
-Fire Blast
-Stone Edge
Nature: Naughty
EVs: 224 Atk/32 SAtk/252 Spe
Item: Garchompite
Yes, the above set has the same moves as your current Garchomp, but the Special Attack EVs let it 2HKO physically defensive Hippowdon with Draco Meteor + Earthquake.
You're doing defensive Tyranitar wrong. It has to use a Sassy or Careful nature with 252 HP/4 Atk/252 SDef to make the most out of the sandstorm it induces. It shouldn't use a Jolly nature unless it's using Dragon Dance or Choice Scarf. Below sets should show what I mean:
-Stone Edge/Rock Slide
-Crunch
-Pursuit
-Fire Blast/Stealth Rock
Nature: Sassy/Careful
EVs: 252 HP/4 Atk/252 SDef
Item: Assault Vest/Leftovers
Ability: Sand Stream
or
-Stone Edge
-Crunch
-Pursuit
-Earthquake/Ice Punch
Nature: Jolly/Adamant
EVs: 4 HP/252 Atk/252 Spe (Jolly) or 180 HP/252 Atk/76 Spe (Adamant)
Item: Choice Scarf (Jolly)/Choice Band (Adamant)
Ability: Sand Stream
What's the point of Aegislash having Swords Dance when Sacred Sword is its only physical move? Some Aegislash function just fine without King's Shield, as the move is somewhat easily played around:
-King's Shield
-Shadow Ball
-Sacred Sword/Shadow Sneak
-Iron Head/Shadow Sneak
Nature: Quiet
EVs: 240 HP/252 SAtk/4 SDef/12 Spe
Item: Leftovers
or
-Shadow Ball
-Shadow Sneak
-Sacred Sword
-King's Shield/Iron Head
Nature: Quiet
EV: 252 Atk/252 SAtk/4 SDef
Item: Leftovers/Life Orb
or
-Swords Dance
-King's Shield/Shadow Claw
-Shadow Sneak
-Sacred Sword
Nature: Adamant
EVs: 240 HP/252 Atk/4 SDef/12 Spe
Item: Leftovers/Life Orb
or
-Swords Dance
-Autotomize
-Shadow Claw
-Sacred Sword
Nature: Adamant
EVs: 84 HP/252 Atk/4 SDef/168 Spe
Item: Leftovers
or
-Autotomize
-Shadow Ball
-Hidden Power (Ice)
-Sacred Sword/Iron Head/Flash Cannon
Nature: Rash/Modest
EVs: 88 Atk/252 SAtk/168 Spe
Item: Life Orb
Bulky Wash Rotom should use the EV spread of 228 HP/60 SAtk/220 Spe. This spread outspends Timid/Jolly base 70 Speed Pokemon and neutral base 80 Speed Pokemon, KOs Mega Pinsir with Volt Switch or Thunderbolt after Stealth Rock and avoids the KO from things like Keldeo's Secret Sword. What purpose does Rotom's EV spread accomplish? When EVing your Pokemon, always make sure that the EVs you put in a stat are divisible by 4, because a stat goes up by 1 every 4 EVs (assuming level 100).
4 HP/252 Atk/252 SDef is the more efficient spread for Assault Vest Conkeldurr. What KOs does Conkeldurr avoid with 12 Defense EVs?
In the last slot, Bug Buzz or Thunderbolt is the better option over Iron Head. The former is a reliable Bug STAB for Genesect, while the latter hits Azumarill, Keldeo, Charizard Y and Talonflame (last one on the switch).