I think one of the most under appreciated things about Kuzan is the use of non-linear story telling with his character.
We meet him in the middle of his character arc and then go back to beginning in the O’Hara flashback with him letting Robin live to test the government’s dogma.
And now we see him with Teach and once again, we are missing another part of his arc (his current motivation).
It’s actually wild how much character work Oda has done with him.