Ron,
All I can say is in my basic premise that one could reasonably consider having all the WDH including the drawbar attached to the trailer tongue and similar to a HA insert that into the receiver and in my view all that wt. would be then considered "TRAILER TONGUE" and "RECEIVER TONGUE" weight. The end effect is the same ... it's temporary wt. in the leverage area of the tow vehicle that is and will be redistributed by the WDH just like the "dead tongue wt. of the trailer itself". I see do difference in the two wts. with respect to the WDH system used. Sort of like this cargo behind the axles. Any non fixed temporary weight that is added behind the rear axle on a TV is subject to being redistributed by the WDH system when used and really no different than the "temporary" tongue wt. from just the trailer. One caveat is that this cargo wt. doesn't translate one to one to additional "TONGUE WT" since that is a function of the distance of the wt. from the rear axle of the TV and the it's distance from the ball or more accurately the fixed end of the WDH bars on the hitch head which are basically at the position of the ball. Your point about bringing the vehicle back or close to the same heights IMO still has to account for the weight of the WDH and the cargo behind the axle and in general those two won't change the measurable heights like the much higher tongue wt. from the actual trailer, but are still weights that have the same class of leverage as the trailer tongue wt. on the vehicle at the receiver. The one, two, three hundred pounds that we are talking about in general and insignificant by them selves, but are still there and will be acted on and redistributed by the WDH just as the much heigher "TRAILER TONGUE WT" will.
All I can say is you asked for some outside information and that is what I provided and I guess you can disagree, but I put the same challenge to you and for you to provide some verifiable independent information from you source to counter what e-trailer has provided. I'm not saying you are wrong, but I don't feel you have proven what e-trailer is saying wrong or incorrect either.
BTW I'm not going to look for it, but I remember seeing similar opinions on this cargo topic behind the axle from other sources, but have never seen a source saying cargo added behind the axle has no effect on the tongue wt. seen by the receiver and can be ignored.
Larry