It's hard to argue against this without sounding 'pro-racism', but I'm giving it a shot. Devil's Advocate or just a prick? You decide!
If the majority of the designers are white -
if the majority of their market is white -
isn't it perfectly natural that the majority of the models they use are white? I don't think that's evidence of racism.
Do countries outside of the West have the same moral obligation to use models of all ethnicities? If we were to tell Japan for instance, 'you MUST use a variety of different ehnicities in your advertisements, or else you're being racist!' Wouldn't that be 'cultural imperialism' or 'subjugation of 'the Other''? It sounds absurd on the face of it, but isn't it in principal the same thing this essay is arguing for?
You could argue that in a multicultural society it's unconstitutional to hire someone based on race. Not hiring someone for an engineering job based on race is one thing. But, if the job is your appearance, it's not discrimination to choose who you hire based on ethnicity.