I think both of you are missing the point.
The author isn't saying Chang is a bad person. And obviously the article is about the author's insecurities and problems with being defined by his race.
"Own what you are and stand by it"
The point is that Chang didn't help the author do this; instead he chimed with the stereotypes that the author was trying to escape.
It's no problem for Chang to do that, since that fits fine with who he wants to be. That's not putting Chang down. But the theme of the piece is that just because a breakthrough celebrity has the same race as you, doesn't necessarily make it easier for you to "own what you are". In this case, it made it harder rather than easier, because the stereotypes the author wanted to escape from were strengthened. That's the irony that makes for a classic Slate contrarian article.
So there's no point saying "Chang is actually a nice guy" -- of course he is. Or, "This style of play is valid" -- yes, it works, but that's precisely the problem for Huan. Or that Huan is uncomfortable with certain aspects of Chinese American culture -- well, obviously, or he wouldn't have written the article. The point isn't to take Huan seriously that Chang "ruined" his pro-tennis career -- that's just hyperbole for the sake of a laugh. The central idea is the meditation on race, celebrity and individuality.