my understanding is , while it can vary depending on the shaft EI profile, the primary goal of soft stepping ( and hard stepping )is to manipulate flight
also as far as I know soft stepping reduces flex by about 1/3 a flex so not sure if thats a typo or not but soft stepping twice wont get you from Stiff to A, but from Stiff to R+
here is a Wishon blurb
""The main reason for soft stepping or hard stepping is to change the feel of the shaft for golfers who really want their shafts to feel just right. The second reason is to try to change the launch angle and trajectory of the shot or to reduce or increase spin. A ½ inch can exhibit the beginning of a ‘feel’ difference. At an inch, some golfers who have a very consistent swing will start to notice some difference in launch angle and/or spin. But in my experience, soft stepping or hard stepping is done far more for the purpose of image than for real performance purposes."
if one is building a set, why not just start with buying the most suitable flex shafts ? If trajectory needs tweaking, soft/ hard step