Weight distribution is not specifically for keeping the rear of the tow
vehicle from squatting relative to the front of the tow vehicle, though
it does do that. The purpose of WD is to distribute the tongue (and tow
vehicle cargo) load as evenly as practical among the front and rear axles
of the tow vehicle and the trailer axles.
I figured that with a 700# tongue (and cargo) load and no WD, the rear
axle loading of my Chevy Express would increase by 953# and the load on
its front wheels would decrease by 253#. With perfectly adjusted WD the
load would be spread among the three sets of wheels by 233# on each. Of
course to get perfect adjustment would require screws on the hookups,
like on a Blue Ox WD spring, instead of using the chain links for
adjustment. We can get pretty close with chain links, though.
With the 1-ton long wheelbase van and no WD the rear hardly squats at
all, only about 1/2", and the front of the van raises by an almost
unmeasurable amount, maybe 1/8".
A 1/2T or 3/4T Suburban would squat and rise more than a 1T vehicle,
especially with its greater rear overhang and shorter wheelbase.
Al