But why is structural power or hegemony considered a prerequisite? Racism exists and has dangerous power regardless of structural factors like legality, see mass shootings. It doesn't need to be institutionalized or dominant to be relevant and dangerous, that just makes it more dangerous.
Just to be clear, I'm of course not trying to equivocate. White supremacy is hegemonic within 'the West', but that hegemony doesn't prevent other racial supremacy movements from local dominance, or even from members performing lone-wolf racially-targeted shootings as an extreme example.