Sorry if I get a bit vague. This topic brings out some folks who seem to be rather possessive of their views and beliefs and are not open to thinking about anything that challenges them. That can create a painful discussion.
The concern that I am coming to is with overly tensioned WD bars, do you put too much stress on the TT frame/monocock(sp?) to where you just do more damage than good?
You have a good measure for the damage (rivets coming loose). That raises the question of whether you have a measure for the beneficial side of the problem to balance against the adverse effects.
A friend was having problems with the cushions bouncing off his trailer couch while going down the road. He dumped the load leveling and now the cushions stay put. As an additional benefit, his ride is much more pleasant, especially when on rough roads like I80 over Donner Pass. He has a measure for the 'beneficial' but it is qualitative and that displeases some.
what is the real purpose of WD and is it to restore weight to the front axle, level the towing assembly, move the weight of the tongue to the TV?
These raise the questions: About why you might need weight on the front axle; About what is a reasonable drag or droop in the TV for the loads it is designed to carry; -- The last one isn't quite right as tongue weight is carried by the TV anyway, a load leveling system moves it forward to the steering axle and aft to the trailer axles.
InlandRV Andy is quite adamant about what shock loads and vibration do to an Airstream in discussions with those who figure more is better when it comes to spring bar sizing. Some use devices like the Centramics balancers to help reduce vibration but that doesn't help shock from oversized springs.
The real question is about the purpose of weight distribution. Perhaps one way to consider that is to extrapolate it to an extreme. What is the effect of a lot of weight on the extreme rear other than just being off level? What would it do to the driving experience? What would a reasonable driver do to compensate? How could you measure this effect directly?
(note, been there done that with a friend I helped to pick up a lot of surplus wharehouse shelving. The drive back with an overloaded pickup across Connecticut was 'interestiing').
The spring bars in modern hitches are only one way to address the issues raised by load distribution. There are others, mostly involving choice of tow vehicle and its suspension. Improvements in automotive design have opened up options in the latter that many have not grasped (accepted?) as of yet. Load leveling with spring bars is being superseded (in part) by technology and many find it hard to part with the past and explore new ideas and new options.
The key is that your hitch must do something for your driving experience. Can you notice what this is? Can you measure it in some way? How much is in your head and how much is in your hands or the seat of your pants? How much is illusion and how much is a real contribution to your driving?