I agree that Rainbow Road isnt the most consistent deck, but with Volcanion EX, it's much easier to hit the 250 number without Sky Field. Say you use Tapu Lele for Brigette. With Brigette, you grab an Xerneas, a Joltik, and a Pawniard. You bench Volcanion, and attach to your active Xerneas (1 is active and 1 is benched). Next turn, attach to Xerneas again, evolve to Bisharp and Galvantula, and that's 250 damage without Choice Band on the second turn of the game. This won't happen all the time either, but it is realistic that at some point of the game that will be your board state.
I forgot about Bridgette, but Volcanion is a nice, juicy worm for the Guzma Fish.