Are you suggesting that character development for Kylo is only recognized when he permanently kills something? Because the way I understand it, you recognize character development by actions, not the extraneous circumstances surrounding them. Especially if they only reveal themselves later on down the line.
I mean, if it was revealed that the guy he killed in TFA was actually a clone of Han Solo’s cousin and his real father is still hanging out somewhere else, I guess you wouldn’t think that affects the scene in TFA or Kylo Ren’s journey at all(?)