Kankri actually didn't have a lusus though, right? I thought he had been raised by some highblood because his blood color indicated he needed to be "coddled" or something

Yes, sorry I forgot to mention that. No lusus would chose a mutant to rear unless they were genetically modified like crabdad was. Kankri was most likely raised by a highblood since he was a lowblood and that’s what being “culled” meant in Beforan society.