Nope. Not alone. I've always done this and actually, I've always assumed it was what most people did. When I was real young (as in during the first Gen), I would train my starter Pokemon to be a WAY higher level than everyone else... after the first time I lost miserably to the Pokemon League, I learned why that was a bad idea. From then on, I trained my Pokemon evenly. When one levels up, I switch his position with the next Pokemon I want to level up. When I'm in a gym, one (as in the one with the type advantage) might shoot three or so levels higher than the rest of the team, and he'll go to the bottom afterward until the rest catch up. On Platinum, with the way there are double battles, I even have it set up to where I'm training Garchomp and Gyarados at the same time because they compliment each other.