Hi, this is a pretty much standard rain offensive team, i have to admit that i have a team with the same pokemon.
However, i feel like you need something to stop pokemon from setting up stealth rock, for example a deo-d lead. I dont know if Stealth rock+Sword dance really works on terrakion because if you do stealth rock then you probably have your sash activated, and if you do sword dance then you have no Stealth rock on the field. So i cant tell you everything else rather than to put the standard Taunt
on Terrakion, in this way you can prevent others thing to setup on you.
Also consider Hidden power Grass
instead of perish song on Politoed to hit Calm rotom-w, which seems a bit problematic since Latios cant switch-in on it if your opponent has a ttar (which is really common). If you do this make sure to put more evs in speed to outspeed Rotom-w, use this spread EVs: 120 HP / 252 SAtk / 136 Spd
with a modest nature. Good luck and hope i helped!
Ps. You have timid Tornadus-t, im sure its a missclick, put naive!