I personally think she is more well written than Kai. Now before you grab your pitchforks, just hear me out. Kai is definitely cool. He has a great theme score, stunning action sequences, and great comedic performance by JK Simmons but I think Chameleon is a better thematic foil to Po. Kai's backstory has some weak points and he did not feel like a good parallel to the movie's themes. Po has to become a teacher and recognize individuality and Kai wants power and revenge, the two arcs don't align. On the other hand, Chameleon directly contrasts Po's journey and the movie's themes of change and mentorship.