I am going to go out on a limb and say that Damian has some the best character devolopement in the Bat family because everyone else suffers from the typical comic book character arc that is losing a loved one and having PTSD incidents throughout their story. Damian on the other hands has none of those and focuses on his journey to be more human, which goes in line with him maturing along the way. Dick and Tim and even Jason were outsiders brought into Batman's world, but Damian was born in it.