I see now. I suppose fitness is an overloaded term, but in terms of survival of a species, I think it'd be difficult to argue that an r-selected reproduction strategy is better than a K-selected reproduction strategy in terms of improving fitness.

That'd be like saying antelope are more adapted to their environment than lions.

In human terms, I'd argue that K-selected children are much more likely to make the types of breakthroughs that will advance the human species e.g. curing disease, scientific discovery, space travel, etc.