Would they have done even better without the racism? Or what accounts for the difference?
That isn't to say that other ethnic groups don't deal with racism too. But it's different. An African American executive in a suit may be mistaken for being a waiter, but he's unlikely to be asked where he's "really from" like an Asian American.
How can you say this with complete certainty? How could you ever be sure?
I think it's easy to point at something like slavery as the underlying cause, but Europeans had no issue looking down on blacks before they had the idea to import them to the new world as slaves, and Europe adopted similar attitudes toward blacks with no slaves present.
Then name the events.
I happen to think that slavery shaped American culture and American history. I find it improbable that a country would have race-based chattel slavery for several centuries but no significant cultural baggage. If that were the case, why then did the South fight Reconstruction? What was the purpose of Jim Crow? Those were concerted efforts to undermine the freedom of black people in particular. If there were no baggage, why didn't everyone just let bygones be bygones?
> Europeans had no issue looking down on blacks before they had the idea to import them to the new world as slaves
Even if that were true, it would not negate my claim. Europeans could have generally "looked down on blacks" before and then created specific slavery-justifying stereotypes about blacks as slavery became profitable.
> Europe adopted similar attitudes toward blacks with no slaves present
There were slaves in Europe. In fact, the British empire didn't abolish slavery until 1833. But even if there weren't slaves in Europe, that would not have precluded intercultural transmission of negative stereotypes about black people. There was little black slavery in Asia, but you'll find many of the same stereotypes about black people there. Countries don't exist in a vacuum.
I didn't claim to know the answer, just that your claims lacked support.
Of course slavery shaped American history, and thus its culture, but step back and imagine it never happened. Let's say the first blacks arrived in the US in 1990.
I'd still expect a similar level of racism toward blacks, because that's true globally. Even people in somewhere like rural China who have never met a black person are likely to look down on them.
Some of the Southern goofiness would be gone like you point out, but overall I'd unfortunately expect a remarkable similar situation.