The question this article raises for me is whether the strategy of out-breeding every other culture is going to continue to be a successful one at cultural leve

The question this article raises for me is whether the strategy of out-breeding every other culture is going to continue to be a successful one at cultural level in the near future. The article suggests that it was, at least in the distant past. It seems like the most successful cultures today (measured by standard of living, anyway) are no longer those with the fastest-growing populations. China (strictly speaking a nation and not a culture) explicitly embraced a policy of slowing population growth, but I'm not knowledgable enough to have an opinion on how complete a success it has been. The interesting thing about culture in the modern age is that it is increasingly divorced from the genetic makeup of its members. If someone who is genetically foreign (to the extent that such a thing is possible) moves to the US and assimilates, their "home culture" has lost a member and "American culture" has gained one (leaving aside the plausibility of this scenario the current insanity of the US immigration system). If this "cultural switcher" phenomenon is large enough to overwhelm birthrate effects we could see culture shaped by some very different forces than in the past.