No. Not an opinion - you brought up "scientific surveys proves". That's not an opinion - either you can prove that claim or you made it up.
I couldn't care less whether there's a difference in size - I just haven't seen a real survey supporting that claim.
There isn't one tiny, you are quite right...
(Pauses to smooth down bleach- blonde beehive and put intellectual hat on)
Mostly the idea of the black "super penis" came from racist ideas: colonialism and then slavery in the American an south. The English adventurer Richard Burton ( who toured India's gay brothels in the 1840's) was obsessed with this.
In the 40's, Kinsey (a famous sexologist), conducted a study that he said found blacks were bigger than whites,-although the biggest dick he'd seen was white- but it wasn't published in his book "Sexual Behavior In The Human Male" and isn't to be trusted.
There was a modern version of these ideas published by J.Philippe Euston, a prof at Uni.of Ontario. But he said that black men were less intelligent than whites to make up for their penis size, and his work is totally discredited as racism.
Porn, cuck, swinger and hotwife culture portrayals/"stats" on line are not science, as you say. They're not all racism though, as some come from a part of empowering black culture and are "reclaiming" the BBC idea.
Undoubtedly black men with big dicks are pervasive and very high profile, but no one knows if on average black dicks are larger than white.