You know, a thought occurred to me when the subject of fertility and an MC's genes permeating the world populace came up in another thread ...
First is that the MC is adopted royalty and has high magic talent and even more potential than he's shown, will live a long life and pass at least some of that longevity to his children, and is considered attractive both visually, socially and (once someone gets to know him) emotionally.
Second, since the curse severely limits the male births rate, not only will he have a large harem, but likely any male kids he produces will also have large harems of their own.
Lastly, his current harem is already huge. It includes princesses and priestesses, elves and enchantresses, soldiers and saviors, commoners and adventurers, etc. And his prospects appear to potentially include queens, duchesses, bandits, tyrants, djinn, dragons, other exotic races, and maybe even demons.
Basically, even if the curse is lifted in his VERY LONG lifetime, his genes could permeate all living sentient beings before he dies.