>>14735890And there lies the cunning of the Elf, sirrah. Elvish males are sociable, promiscuous, typically desirable to impressionable human girls, and struck constantly by wanderlust. It is likely that one will mate with between 80 and 120 human women in its life, of whom a considerable number will produce offspring. Half Elves.
These halfbreeds are absorbed back into human society for lack of anywhere to go, but this introduces elvish genes everywhere amongst humans, genes which will, over time, compound thanks to their own rapid breeding, moving the human race towards a mean of elvish genetics. Over time, in fact, with repeated introductions of elvish blood, the population may become part-elves of varying degrees.
So, when the time to finally genetically overpower the humans comes, it will really be more like genetically overpowering half elves. The equation strongly favors the elves, so long as they guard their womenfolk and take the long view, something at which they excel if little else.