Nice team, this team of yours. Whirlpool in Politoed seems really good, especially because Poli have Perish Song, something Fire Spin Ninetales dream to have.
So, I would work around this Politoed of yours. With Whirlpool you can trap a lot of things that wouldn't be able to damage your sweepers at all; this said I would change Gyarados set. This said, a Substitute DDance Gyarados
would be a better option. Why? Because by traping things like opposing Politoeds, Ferrothorn and most walls that can't phaze (like the pink blobs) you can set a couple of Dragon Dance and sometimes a Substitute and go for the sweep. You could even run a Lum Berry instead of Lefties to avoid statuses on the switch.
Another thing is swaping Cloyster for CM Latias,
mainly because your team lacks special attacking pokemon. And just like Gyarados, Latias can abuse the trapped pokemon to setup and sweep; also, Latias is a good check for sun teams too, something you say can give you some problems. The last move slot depends of what you want to counter the most: HP Fire is nice against sun teams, while Psyshock wins CM wars (meaning you will always win against Keldeo) and either Refresh and Substitute is to deal with status.
Last thing I wanted to point out is that your team could abuse of a Amoongus+Slowbro defensive core, but for this you would have to give up Tentacruel, which is your spinner. This is up to see if is worth.
Good luck with your team!
change to this set
EVs: 56 HP / 248 Atk / 204 Spe
Adament Nature (+Atk, -SpA)
- Stone Edge/Bounce
- Dragon Dance
change to Latias
Latias @ Leftovers
EVs: 252 HP / 4 SAtk / 252 Spe
Timid Nature (+Spe, -Atk)
- Dragon Pulse
- Calm Mind
- Substitute/Refresh/Hidden Power Fire/Psyshock
Regenerator core (maybe)