Scales have been used in kitchens, including American ones, since the invention of the scale, several thousand years ago. I own cookbooks dating back to the early 1700s that use weight based measurement. My mother owns a kitchen scale with date in the 1840s stamped on it. Farmers, tradesmen, professional cooks, and many others used scales in their homes and businesses on a daily basis to buy and sell commodities and wares.
Sometime around 1900, US publishers decided to drop weight based measurement while publishers in the Britain, France, Spain, Germany, Russia, Italy, Mexico, Brazil, Argentina, Egypt, India, Pakistan, South Africa, Greece, Japan, China, Korea, The Philippines, Australia, New Zealand, Canada, and many more countries continued to publish weight-based recipes for home and professional use.
The recipes he wants to convert aren't really all that old, they are, however, poorly written by authors who did not take advantage of readily available technology. Would you sous vide meat to done-ness based upon just the feel of the meat compared to the feel of the base of your thumb, without the use of any thermometers? If you found a recipe written telling you to just use touch instead of a thermometer in sous vide would you trust it more than tips from a chef instructor with years of experience using thermometers who tells you to use a thermometer for more accurate results? Would you keep asking questions of the chef about your ongoing inaccurate results using the thumb method after ignoring his advice several times? That would be Dunning-Kruger in action.