"They just found the best actor for the job" is really the laziest, least interesting possible answer to a complaint about whitewashing, to the point where I'm basically willing to call it just a derailment tactic. Because of course that's always the excuse and, as J_M points out, the "best person for the job" turns out to be a white guy a suspiciously disproportionate amount of the time.
It's basically like saying "Has it ever occurred to you that most CEOs are white men because white men are just smarter?"
It's basically like saying "Has it ever occurred to you that most CEOs are white men because white men are just smarter?"