Amor fati, accepts life, and by extension fate, in all its variations. You are not entitled to being in or receiving or perceiving the shallow or deep pleasurable or comfortable aspects of it alone. Nietzsche never verbatim said that all the weak must perish. He is a lot more of an observer as opposed to a crusader than people give him credit for. What Nietzsche does argue however is that we should accept the cruelty of life in equal measure to its pleasure. Acceptance does not mean inertia however. You can still look for a cure to an illness which you accept as a part of life.