Where did we get the idea that a car/truck dealer should know about hauling a TT.
Yes you can get a F-150 equipped to tow 11,000 lbs. but with that tongue weight you can haul little more than the driver and keep within the max cargo limit.
The dealer sees a 500 lb. tongue weight and thinks your TTs 450 lbs. is fine. He does not know about your kids, bikes, camp gear and other stuff or that you need a WD hitch to make it ride level.
Yes it is true that sometimes folk tend to be a little critical, but that is because they have been at it so long they forget it is not so obvious to others.