Racial diversity is orthogonal to ethnic diversity. It shouldn't be code for "Black".
For example, continuing with your Atlanta example, the city of Atlanta is 84% white and black, and those White and Black Americans in ATL are overwhelmingly of southern origin in the US.
Meanwhile, an Asian American from Jiangxi is extremely different from someone from the Mekong Delta who is extremely different from someone from Jeolla in South Korea. The only similarly they have is looking kind of similar.
Same for Latiné communities as well.
East Coast cities have more "White" and "Black" people, but not as many Asians or Latiné.
Also, you have to remember the history of the Western US - much of the US west of Dallas wasn't part of the US until the 1840s, and remained a frontier backwater until WW2, so a number of Asian and Latiné ethnic groups had a longer history here than a lot of ethnic groups that are now pivotal in the US.