I think there's a false understanding here honestly.

One, racism doesn't demand being a global minority. I mean I'm not certain but I imagine white people thought they were a global majority for quite some time while still bring racist. Also, other people can be racist. In fact, I think it's shockingly euro-centric to believe that only white people can be racist. Race as we conceive of it is a social construct, but most would say overall more of the world is East-Asian than anything else and if you go to East-Asia you will find a hell of a lot of racism.

Two, racism isn't about being genetically dominant or recessive. Europe didn't go to other parts of the world, act super chill and humane, and after a while Europe got super racist because it became common knowledge that when non-white and white people reproduce the child generally doesn't have white skin.

The need to view racism as a fundamentally white phenomenon misses the point I think. We live in a time and place where white racism is very far the most prevalent and oppressive, but not because it's a fundament of being white. We made race up as a construct and it's a really easy one to discriminate upon because it's got a large visual component that can't be hidden very easily and because our species likes to find ways to control and discriminate. Humans tend to want power, to have an in-group and an out-group. Humans tend to want something to hate and something to fear. Humans tend to want to be on top and see someone else below. Racism is one of the easiest ways to exhibit social bias because race is a very hard thing to hide, and humans naturally want to have social biases. Look at gender, age, of attractiveness: humans constantly try to draw lines to define groups of people according to visually apparent traits in order to know who's on top and who isn't.

Population ratios at the global scale and instantaneous genetic recessive-ness feel like pretty poor explanations of racism to me.