The format of your post makes it look like you are trying to build a case. Not sure what it is, though.
If the Chiyuv is Deoraysa then since we don’t go by Taamei Dikra we don’t change our decide Halachos based on the reason for them. In fact we assume that we never really know the while reason for a Mitzva in the Torah.
If it is Derabanan, or Asmachta, then we do pay attention to the reason. This is why by Derabanans we say Af Hen Hayu Be’oso Haness. That is why woman are Mechuyav in Megilla and the Arba Kosos.
This is a Talmid’s attempt to be Meyashiv a Rebbi’s Chakira, which is why I prefaced it with, “I would say.” The Ksav Sofer probably understand these reasons to be the complete reason, which means that he understands it to be Derabanan.