Sizing weight transfer bars too high can damage the vehicles and create harsh rides.
My 27-foot trailer has a sticker on it warning against bars heavier than 1000 pounds. It has a 900 pound hitch weight and I use 800 pound bars. Perfect for me.
Some trailers have been damaged by bars too heavy, with cracked frames, popped rivets and wrinkled bodies not to mention the buck-wagon ride.
I've been told that most properly sized weight transfer bars are designed to be used with the "bend" in them. This provides a spring action that is good for the ride.
Yep, too much medicine is not what the doctor ordered.
About the ball size: this is the most elementary mistake that can be made. Where are the "professionals" getting such "help?"