This is true along with other factors. Many folks are using cross bikes for touring which have shorter(<45cm) chainstays , Many newer racks are offset to the rear of the axle to compensate for shorter chainstays and/or disc brakes. Many racks are mounted way too high.( should just clear the top of the fender or ~1" above the tire). Many panniers have poor or non existed lower hooks to keep the bags from swaying. Traditionally tourists sat an spun the pedals in a low gear up steep hills, not stand on the pedals and rock the bike like a sprinter.

All of that said touring bikes do handle better with a fore/aft balanced load.