Duncan Hines and Betty Crocker got their recipes from housewives and local independent cooks. They gradually made them cheaper to make or they substituted their own products like Ketchup for tomato sauce or Bisquick for eggs and flour. But they did start out as recipes people loved, turned into commercialized versions and back into loved recipes.
I always use and consult two recipe books. One is the book from the 1960s which always uses things that are in the average housewife’s kitchen from the 1960s it often uses corn flakes instead of starting with flour. (either Joy of Cooking or Betty Crocker are fine)
I then use a recipe book that researched the original versions of recipes from the 1800s before most of these products were invented. You start with tomatoes to make tomato sauce, not a can of tomato sauce. I look at both recipes and decide what short cuts I am going to take and where I want to go with the original. Original recipes often use lard or butter, never corn oil.
I started on an old cookbook quest when the White House Cookbook was reprinted in the late 60's. I made a hot chocolate recipe exactly as listed - only to discover that the ingredients had become more concentrated over time. It was still an excellent, if thick hot chocolate drink.
There are a few YT channels that look at recipes and how they have changed over time, especially as artificial leavening was created and started being used.