Fard, wajib, sunnah and nafl are distinct categories of prescribed conduct. Haram, makruh tahrimi and makruh tanzihi distinguish forms of prohibition or disapproval. The book's Hanafi presentation differentiates fard from wajib by the conclusiveness of the evidence. All disliked acts must not be treated identically.
Azimah is the original governing rule, while rukhsah is a concession for a recognized excuse. The book distinguishes concessions that leave the underlying prohibition in place from those granting limited permission under severe necessity, such as preserving life. Application depends on actual conditions.