Not at all. You see, Ditto was considered horrible before Gen V because it didn't have reliable Transformation. Ditto was much too slow to get in a Transform, and usually it ended up getting OHKOd. Eccentric makes it Transform as soon as it enters into battle, plus it gains any stat boosts the opposing Pokemon got. Combined with a Choice Scarf, this means he is an amazing revenge killer, almost always able to hit first.