You are doing well to dismiss it. All hitches have a weight rating for tongue weight and trailer weight. Actual trailer hitches generally have higher ratings than a ball on a bumper, but have their limits none the less.
Also, just because a hitch has a certain rating on it, doesn't mean your tow vehicle has the same ratings. Some half tons (mainly from pre 2010) had the same hitches as a 1 ton truck. Also, hitches have 2 sets of weight ratings. One rating is for a weight distributing hitch (higher rating), and the other is weight carrying.
Also, if your dealer is telling you that malarkey, I would find a new dealer.