Well....no. Rare Candys are usually only useful for leveling up just a bit, or if you've already EV trained. A Pokèmon trained completely with Rare Candys will lose very often, because Rare Candys don't always give good stat boosts, and no EVs are gained. No EV training=Not as powerful. Since it's in-game, and EV training doesn't really matter that much, just battle to level it up instead. By battling, you are technically EV training anyway, you just won't get specific EVs.