What tweaks could I make to my team to make it more viable for OU?

Question

Dragonite @ Weakness Policy
Ability: Multiscale
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Dragon Dance
- Fire Punch
- Earthquake
- Extreme Speed

Heatran @ Leftovers
Ability: Flash Fire
EVs: 4 Def / 252 SpA / 252 Spe
Modest Nature
IVs: 0 Atk
- Magma Storm
- Earth Power
- Taunt
- Stealth Rock

Scizor-Mega @ Scizorite
Ability: Light Metal
EVs: 248 HP / 252 Atk / 8 SpD
Adamant Nature
- Roost
- Bug Bite
- Bullet Punch
- Swords Dance

Greninja @ Choice Specs
Ability: Battle Bond
EVs: 4 Def / 252 SpA / 252 Spe
Timid Nature
- Hydro Pump
- Dark Pulse
- Water Shuriken
- Spikes

Gastrodon @ Leftovers
Ability: Storm Drain
EVs: 248 HP / 8 Def / 252 SpD
Sassy Nature
- Scald
- Recover
- Toxic
- Earthquake

Tornadus-Therian @ Rocky Helmet
Ability: Regenerator
EVs: 252 HP / 4 Def / 252 Spe
Timid Nature
- Hurricane
- Knock Off
- U-turn
- Defog

Comments

Good team overall. I was going to knock Gastrodon, but I can see why you're using that over Toxapex given the weaknesses double-ups it would have created.
I haven't used Dragonite in forever, but I think the current state of affairs says Weakness Policy is a gimmick. The standard DD set involves Fly + Flyinium Z; I'd at least give that a try before continuing with the WP set. I'd also consider using U-Turn instead of Bug Bite, as the latter has a lot of crossover with Bullet Punch, and U-Turn can allow guaranteed safe switches into Dragonite or Greninja.

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You have a lot of 4x weak Pokemon. You'll give your opponent easy pickings.