As stated in the article, it's not that genuine cosmopolitanism doesn't exist- it's just rare. I'd be somewhat hard-pressed to find a political ideology that does not consider itself to be superior to the other ideologies, one in which the majority of members follow the 'full' ideology rather than a watered-down version. This article seems to be complaining that cosmopolitanism suffers from the same issues as any other ideology, and while that does not make the complaints invalid, it does raise questions as to why it's specifically cosmopolitanism that's being called out on this.
I may be missing something here, or misinterpreting some section, though, so please correct me if I've said something wrong.