That picture is misleading. Although the pain relief effect of carfentalin is ~35 times higher than fentanyl, the lethal dose of both drugs is about the same. So carfentanil is actually safer, in the sense that it has a higher therapeutic index.
Botox is lethal at ~1ng per kg of body weight. It takes 20,000 times that amount of the compound in question to kill you. (These are both using LD50 numbers).
Botox is a refined form of one of the most lethal substances to humans, it is a poison, and most of all it’s not a recreational drug of abuse commonly smuggled around the world. You also can’t absorb it through your skin like fentanyl and carfentanil. Brief contact with botulinum toxin won’t kill you, but brief contact with a rice-grain sized particle of carfentanil can and will.