It specifically
was chosen to avoid "lower class" usages and things like AAVE (though
that term would not exist for decades after the movement reached a
furor).
I mean, surely not only did it exclude "lower class" terms and AAVE (African American vernacular English, for the rest who don't do well with acronyms) it also excluded a number of dialects used by groups of all colours and backgrounds. I don't think I'd find any Australian words in there nor any Scottish ones, would I?
I don't see how standard English is a white supremacist construct. I see it as an intersection of most of the dialects around, as a means to optimize communication by following a common set of guidelines.
Can you elaborate on why you view this as being white supremacy?