I am not an engineer BUT it seems to me that somewhere in my history (almost 70 years) I read that the reason driveshafts ARE hollow was tha the majority of the strengh is in the "skin" of the metal. Besides the cost savings less mtal to purchase and obivious lighter weight. Driveshafts have a different purpose, but strengh is strengh? Cost difference has to do with many things, where it's made, labor rates, and quanties sold. I just got a used 2016 Ram, that was ordered with tow package - but also - Hitch delete ? So I need a hitch. My Dakota -that the Ram replaced was ordered by me with the"full" trailer tow package (class IV) I put a class V on the Ram, even though it is pulling the same trailer/car combo. Both IV & V were HD enough to do the job. But the Class IV was $395 the V was $229 ( bennin the O'Riellys store way to long - was at the give it away before we have to write it off price. Same brand and size of shoes different depending where and when you buy.
The hitch attaches to the vehicle. The ball mount can be part of a hitch (like a class 1- ball mount NOT removeable , or a seperate piece like class IV and V. the ball goes in the ball mount of course.
GTW - gross towing weight - Varies on all cass IV's & Class V's depending whether you are dropinmg the trailer on the ball or using a "weight equalizing" Coupler.
Bottom line buy and install a hitch that will exceed your needs, not the bare minium - 6,000 lb. rating to pull 6,000 lb. Rule of thumb last time I looked was "recommended" you use equallizing hitch if what is being towed is greater than 1/2 the weight of the tow vehicle. Equalizing "USED" for sure if weight - (GTW -trailer and whats on it or in it) is equal to/or greater than whats pulling it.
This is just BASIC info. call someone like Reese, Curt, etc. that makes and sells this "stuff". to verify the info. Find answers to when a trailer should have brakes, lights required, how AND WHY trailer ball height is determined and set (what parts are needed to accomplish this), how much weight MUST be on the ball - so your trailer does not wave to those on the road that are following you, and on and on. Be safe TOW SMART. Class dimissed you may all step out for a break.