To me it doesn't hurt his character arc because the idea Aang would never make serious mistakes after the series ended was unlikely.

His character arc in TV show is accepting his responsibility as the Avatar and becoming fully realized. However he has no peacetime leadership experience and is still very young, so expecting him to struggle with the morally grey areas of peacetime is to be expected.

You can see in the Legend of Korea that Aang and all the gang change drastically in their lives to fit the roles they take on.