Is Iroh saying if Zhao was more clear headed he would’ve known not to slay the spirits? Simply threatening to kill Tui would’ve been enough to depower the water benders and capture the Northern Water tribe.
It would be nice to have a teacher-student relationship with the avatar, plus the reputation.
Nothing wrong with accompanying Aang for a little while while training him in the basics of water bending, no need to teach him everything of course.