[Padgett]

"I've noticed that the current batch of mid-size SUVs (like Ford Explorer, Toyota Highlander, and Chevy Traverse) quote a standard 2,000 lb tow capacity but a 5,000 lb tow capacity with their tow package. I'm skeptical on how a tow package can more than double the tow capacity."

I can think of several reasons:
1) Factory hitch on mine is a Class IV receiver that slides inside the frame rail rather than being underslung (why I need a 3.5" drop to put the hitch ball at 20") All I can say is that the receiver took most of the impact that totalled the full sized Ford 150 that rearended me back in '12 without taking any material damage.
To mount the receiver required a special cut out fascia panel.
2) Most factory packages include things like rear load levellers, heavy duty radiator, alternator, & extra oil and trans coolers all of which add to the towing capacity. Many also include a lower axle ratio and different wheels and tires.
3) Factory hitch includes a Bargman connector and wiring for the brake controller

So before you doubt that a factory package can double the towing capacity, review just what the package includes, it will be more than just a hitch.