I'm completely new to competitive team building so I'm still trying to get a grasp on the meta as well. I'm assuming Swampert is too slow for those particular matchups. I'm not sure how to build them to be honest.
Bisharp @ Life Orb
Ability: Defiant
Level: 50
EVs: 4 HP / 252 Atk / 252 Spe
Adamant Nature
- Sucker Punch
- Knock Off
- Iron Head
- Protect
Thundurus-Therian @ Choice Scarf
Ability: Volt Absorb
Level: 50
EVs: 4 HP / 252 SpA / 252 Spe
Modest Nature
- Thunder
- Volt Switch
- Hidden Power [Ice]
- Dark Pulse
Scrafty @ Lum Berry
Ability: Intimidate
Level: 50
EVs: 228 HP / 192 Atk / 88 Def
Brave Nature
IVs: 0 Spe
- Fake Out
- Knock Off
- Drain Punch
- Stone Edge
These Pokemon would make a good rain team in my opinion based off the core you have in mind. You can't disguise a rain team because if the opponent sees Politoed and Swampert, it is going to be their first assumption.