^ Or to put Marty's experience into laymans terms, you can tow quite heavy with a smaller truck "if" its the right combination of weight, tongue weight, trailer axle placement, tow rig wheelbase, trailer length, etc.
And you can have issues with a bigger truck if the above considerations are "wrong."
As usual, no one size fits all answer. Hence why those who aren't as knowledgeable or don't care to get into the details often opt to "over truck" the combo, which generally never is a bad thing. Regardless of whether it's necessary or not.