I don't think the person you're replying to said anything that disagrees with your assessment.
> We are committed to combating abuse motivated by hatred, prejudice or intolerance, particularly abuse that seeks to silence the voices of those who have been historically marginalized. For this reason, we prohibit behavior that targets individuals with abuse based on protected category.
https://help.twitter.com/en/rules-and-policies/hateful-condu...
Note the weight of "Particularly" above.
Reddit had a similar policy but recently removed the clause "For example, the rule does not protect groups who are in the majority".
You won't find a relevant textbook in use in major universities that doesn't support this definition, perhaps even explicitly. It would be a brave politician to openly object to this concept.
What is said in private may be different, but publicly this definition has the consensus in the modern West.
They do have a lot of power, so aren't they capable of being racist against white people, even when racism is defined as power+prejudice?
I'm just pointing out the obvious logical mistake being made by generally rational academics and textbook authors. Obviously we don't often see reason triumph over political advantage among politicians and the press, but without the support of educators that redefinition would have far less support.
The dictionary.com definition for racism says nothing about power being a requirement:
A belief or doctrine that inherent differences among the various human racial groups determine cultural or individual achievement, usually involving the idea that one's own race is superior and has the right to dominate others or that a particular racial group is inferior to the others.