You can't compare early Grey's to where it is now. In addition to Bailey and Webber, there are now Avery and his mother, Bailey's husband, Stephanie, and Pierce, along with the Hispanic Callie Torres. Trust me, it's basically an even split now, with most of the fictional hospital's management being people of color as well. Much more diverse now than you're giving it credit for.
And honestly, I think a show like Grey's featuring black actors in roles that don't actually rely on their blackness is much more significant than a show like Empire which features black actors specifically because of the fact that they're black.