Nobody has said that and, even if people had said that, it’s not a reason to deny racial difference. If some people adamantly believed that red apples tasted bitter and green apples tasted sweet, would you try going around trying to convice people that red apples are really green? Of course not, you convince them that there are sweet red apples.
Again, it’s an asinine belief and shouldn’t affect the factual basis of racial difference. Every reasonable person and certainly every athlete knows that it’s impossible to achieve at the highest level without a whole lot of blood, sweat and tears. Innate ability counts for jack if your not willing to use it. However, that doesn’t mean innate abilities do not exist. Would you tell a 5’0" man he has just a likely chance of playing in the NBA as a 6’8" man? Of course not. It’s obvious that his innate height is going to significantly hamper his chances and it would be stupid not to acknowledge that.
Except this hasn’t happened and it doesn’t explain all phenomena. Mexicans aren’t dominating NFL, even though they apparently should be next on the list. And there are plenty of disenfranchised people all around the world who would love to compete in the steeplechase, it doesn’t account for why only a single country actually does well in it. And it doesn’t explain why sprinters come from west africa and long distance runners from the east. Are eastern runners just irrationally prejudiced against sprinting and refuse to even try it? Are western runners not poor enough to consider long distance running? The hypothesis doesn’t fit the facts and must be discarded or amended until it does. That’s how science works.