In the comics, Swinton's character, The Ancient One, was a powerful Tibetan mystic, an Asian man, and 'and a dated stereotype at that' according to the article.
Having the Ancient One cast as female at least marks a step towards progress for Marvel, because of its usual lack of strong female roles. Derrickson says this was the first decision made and that it wouldn't be a '26-year-old leather-clad fanboy dream girl'
Casting an Asian woman felt like contributing to a bad stereotype
"Whitewashing, if you use the term the way it’s used now—it’s what I did with the role. But it also implies racial insensitivity and it implies racist motives and I don’t think I had either. I was really acting out of what I still feel is the best possible choice. But it’s like I chose the lesser evil—and just because you choose the lesser evil it doesn’t mean you’re not choosing an evil."
Talks about reinventing the character of Wong - instead of a sidekick, he's Strange's intellectual mentor
"Diversity is the responsibility of directors."