with respect, simply reducing load does not remove the fundamental design issue with leaf springs - there is no lateral triangulation and thus no lateral rigidity. simply reducing load just makes the problem smaller, it doesn't make it go away.
by way of contrast, we've managed to [slowly] pull our heads out of the sand on engine technology - we no longer have manual ignition timing controls on our steering wheels for example. we need to pull ourselves out of the 19th century and abandon what is in reality horse-cart suspension for our motorized carriages. unless we want to continue to drive at horse-cart speeds and with horse-cart loads.