Chiwetel Ejiofor was not at all even trying to be desi. In fact without the name and the slightest hint of an accent that he had, yes, he could’ve very well been an African-American character.
And The Martian being Irrfan’s big break is way off the mark. Remember Life of Pi, Slumdog Millionaire, New York, I Love You and The Darjeeling Limited. The dude knows good movies and even a lot of his Bollywood movies are big budget blockbusters, but smaller, smarter productions so giving up a bigger movie isn’t that big of a deal for him.
Coming to the point about casting more Indian actors, I don’t really care one way or the other, but this guy is a serious talent and never really seems to get the recognition he deserves.