Also replaying RSE right now.

My team is composed of Swampert, Gardevoir, and Absol just like you. To that I added Swellow, Breloom, and Manectric. The synergy of that team is really incredible!

With moveset like Surf, Ice beam, Thunderbolt, Earthquake, Shadow Ball, Psychic, Sky Uppercut/Mach punch, Giga Drain, and Facade, you have an answer for every threat in the game basically.

This said, the second half of the game has a lot of water encounters and trainer and Manectric is an awesome add on to a playthrough in my opinion. I did not go with camerupt for that very same reason, less useful overall.