I agree with you, but there is a lot of gray area. What about Spider-man? 95% of the pictures it ingests are probably Peter Parker so it would have a strong bias towards making him white when there are several ethnicities that might apply. What about Katniss Everdeen? Is she explicitly white in the book or is she just white because she's played by a white actress? I truly don't know so maybe that is a bad example. What about Santa? What about Jesus? Of all characters, Jesus absolutely shouldn't be white but I'll bet the vast majority of AI depicts him that way.
I'm not disagreeing with you so much as I'm pointing out the line isn't really all that clear. I don't like this ham-handed way of going about it, but I agree with and support the goal of making sure the output isn't white biased just because preserved history tends to be.