It is a very effective and solid team, I appreciate Sandslash with his ability (Sand Rush), speed is multiplied by 2 with the SandStorm, and then with Sword Dance it is awesome, but you are disadvantage against Gengar with Substitute I think, because with the Sub, Gengar can OHKO Tyranitar with Focus Blast, Latios breaks the substitute but it is OHKO by ShadowBall and if Gengar has Energy Ball,GigaDrain, Thunder or Thunderbolt it can kill Keldeo easily, and then Keldeo is 2HKO by Shadow Ball. I suggest you to swap Tyranitar in Choice Scarf, with this item Tyranitar can outspeed Gengar and kill him with pursuit or crunch, but before break the Substitute.
Then you are weak against Rotom-W, even if you have Latios, it can not tank Volt Switch correctly because it does not Recover/Roost and then the opponent can put a counter after Volt Switch to force you to switch, you will be disadvantage, I suggest you Latias Life Orb on Latios, Latias is a very good pokemon for your team, even if Latios is better, Latias Tank better and with the Orb Life it can be awesome, and then Latias has Recover to heal, so it can easily come on Rotom-W. I agree with Novaray, Landorus Rock Polish is your main counter, you can not do anything because Keldeo is OHKO by Earth Power and Landorus outspeed Latios after a Rock Polish, now that you have Latias you can kill him easily.(252 + SpA Thundurus - T Hidden Power Ice vs. 4 HP / 0 SpD Latias: 146-172 (48.34 - 56.95%) - 89.84% chance to 2HKO) and Thundurus-T is OHKO by Draco Meteor.
Now your team is weak against the Entry Hazards (Spike/Stealth Rock/Toxic Spikes) I see that you have Sandslash in your Team, I suggest you Rapid Spinn on X-Scissor because after a Sword Dance Reuniclus is 2HKO by EarthQuake, Latios sweep and Latias sweepalso, Slowbro is 2HKO by EarthQuake with the Life Orb, then you have Volcarona, without spinner he can't set up correctly (50% on Stealth Rock). And then with the Sand Storm Sandslash can spinn easily.
Hope I Helped and Good Luck with your Team.