I think the intensity matters: my Irish ancestors weren’t considered white when they got here but there wasn’t a mass exodus from cities rather than sharing infrastructure, and they were allowed into whiteness over time (especially when large numbers of cops were needed to police black populations). The ones who served in the military weren’t restricted to certain units and duties, etc. When white people moved to the suburbs, the neighborhoods which were razed to make highways had a very uneven distribution.

That’s definitely not perfect (and it’s like, say, Chinatowns weren’t raided or sacked) but that option of coexistence wasn’t on offer in much of the country.