Have just scanned some of the posts on this subject in the past, but aren't they really talking about an additional ancestor of only the Europeans? From some of the other comments, that's not so clear.
There’s a kinda weird unsubstantiated bias, with an origin in the 19th century, that Neandertal died out, that modern humans are gracile and intellectual, while Neandertal was dumb and clumsy. :’)