Electrolyte, this was a fun read! I really appreciate how you were able to fit Cobalion into this team, and it's such a cool set, too :D
As you mentioned Latias and RP Landorus are some notable threats to this team. Although you haven't listed it as such, Volcarona on a Sun team can relatively easily sweep this team, given the opportunity by Latias. Here are some quick fixes to these problems:
Divert 40 Defense EVs into Politoed's Special Defense
. You use Politoed for mixed-walling, so the extra 40 SpD EVs would help tank hits from the likes of RP Landorus, Gengar, or Volcarona. You still reach the jump point in Defense (264).
Try out Water Gem Rain Dance Latios
over Specs Latias. This is a set that shrang has discovered, and I believe it would benefit this team by aiding you in the weather war. After Rain Dance + Water Gem, Latios's Surf virtually OHKOs all but the most specially defensive Tyranitar. It will certainly throw off Sun teams, too!
Latios @ Water Gem | Levitate
Timid | 4 HP / 252 SpA / 252 Spe
~ Draco Meteor
~ Rain Dance
You can use Life Orb if you want, but WGem is recommended to OHKO bulkier TTars with SR
Finally, I suggest replacing Breloom for Mamoswine
. Mamoswine gives you a quick and dirty answer to all the annoying Celebi and Latias that troubles this team with its powerful STAB Ice offense. Even more, it makes RP Landorus a non-issue as you can OHKO it any time. Losing Breloom means you miss out on Mach Punch, but most targets for Mach Punch is covered well by this team (ie Landorus-T checks Terrakion). You also lose out on Spore, so if you really want that sleep support, you may want to try Hypnosis
on Politoed over Toxic.
Mamoswine @ Life Orb | Thick Fat
Jolly | 252 Atk / 4 Def / 252 Spe
~ Ice Shard
~ Icicle Crash / Icicle Spear
Thanks for sharing this creative team, and have fun :)