Chapter22-23

In my opinion, what Amir says means that Assef and he both got what they are supposed to get so I do agree with what Amir says.
For Amir, he has successfully god rid of his coward character and finished the wish by Rahim Khan-taking Hassan’s son safely to a better place. Besides, his behavior also makes up for the sins he did to Hassan in the past to some degree and a way to thank him for his loyalty so that he can get relieved and does not be blamed and feel anxiety for his faults along with his whole life. In addition, Sohrab is his own nephew, the only living kin who has blood relationship in the world after all. Moreover, the injury compared with Hassan gets is not severe but still a kind of punishment.
On the other hand, for Assef, it is absolutely a good lesson for him that he must not bully others all the time. Whoever does evil things will have a bad result. What’s more, it is rather an ending for Amir and Assef’s enmity than a revenge by Assef because he still takes the thing that Hassan and Amir once were rude to him to heart so Assef wants to abuse Amir to make him realize that whoever goes against him will get suffered.