[OU] Team building help

Trying to build a Mega sceptile team at the moment, and finally broke past 1500 on pokemon showdown the other day with this team: Sceptile-Mega (M) @ Sceptilite
Ability: Overgrow
EVs: 4 Atk / 252 SpA / 252 Spe
Naive Nature

• Leaf Storm
• Dragon Pulse
• Earthquake
• Hidden Power [Fire]

Volcanion @ Choice Specs
Ability: Water Absorb
EVs: 252 HP / 252 SpA / 4 Spe
Modest Nature
IVs: 0 Atk

• Steam Eruption
• Fire Blast
• Sludge Bomb
• Earth Power

Excadrill (F) @ Air Balloon
Ability: Sand Rush
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature

• Earthquake
• Rapid Spin
• Rock Slide
• Iron Head

Tyranitar (M) @ Choice Band
Ability: Sand Stream
EVs: 100 HP / 252 Atk / 156 Spe
Adamant Nature

• Pursuit
• Crunch
• Superpower
• Stone Edge

Zapdos @ Leftovers
Ability: Pressure
EVs: 248 HP / 64 Def / 180 SpD / 16 Spe
Calm Nature
IVs: 0 Atk / 30 Def
- Volt Switch
- Roost
- Hidden Power [Ice]
- Heat Wave

Landorus-Therian @ Rocky Helmet
Ability: Intimidate
EVs: 252 HP / 240 Def / 8 SpD / 8 Spe
Impish Nature
- Stealth Rock
- Stone Edge
- Earthquake - U-turn

Rotom-Wash @ Chesto Berry
Ability: Levitate
EVs: 248 HP / 252 Def / 8 Spe
Bold Nature
IVs: 0 Atk

• Volt Switch
• Will-O-Wisp
• Hydro Pump
• Rest

Bronzong @ Leftovers
Ability: Levitate
EVs: 252 HP / 4 Atk / 252 SpD
Sassy Nature
IVs: 0 Spe

• Stealth Rock
• Gyro Ball
• Earthquake
• Protect

Currently, i am trying to figure out the last two slots, my defensive core. Currently my Defensive mon is Landorus T due to stealth rocks, working well in a sand team, and U-Turn to boot. I chose Zapdos because i wanted a specially defensive pokemon with access to Volt Switch to complete the volt turn core. Is there anything that you recommend changing or switching from the entire team or the defensive core? Is there a better defensive core that works well with the previous 4 pokemon that i haven't noticed?

EDIT: changed the defensive core to Specially defensive bronzong and resto-chesto rotom-w