The "majority definition" argument is itself an illustration of the "power + prejudice" argument. As a line of thinking it's suited white America to have racism reduced to something that nasty individuals inflict onto others (that MLK and Lincoln fixed already), as opposed to a pervasive cultural phenomena that benefits them even if they as individuals have no conscious prejudice. This didn't come about fully consciously, because that isn't how societies evolve most of the time, but being the empowered majority always plays a crucial role. If the black citizens of America had by some sociological miracle become the ruling class in the last 150 years, just imagine how different the narrative would be. If you've never before felt compelled to run that thought experiment, congratulations: you just demonstrated the fact of the argument once again.

Fact is, it's impossible to divorce racism from the concept of power outside of the pages of something as narrow in focus as the dictionary. We see white supremacy of varying degrees on reddit all the time. Those few incidents of the reverse are almost always presented by white people to other white people as a form of jingoistic outrage porn: white folks using their control over the narrative to present themselves with anecdotes they'd otherwise never have experienced directly, seemingly to justify the narrative that "black people can be racist."

To talk on terms of smaller scope than this is to fail to define anything remotely useful.