I mean, that has already happened in our history. The result is that the lion’s share of humans are 1-4% Neanderthal. Not to mention ancestry from Denisovans and possibly others.
The end result of a DnD world is a bunch of humans with slightly pointy ears and big teeth.
This is why I’m convinced we need to start mechanically speed-limiting cars. We do it for ebikes, but god forbid we do it for vehicles 100x heavier. No, your 4000lb vehicle does not need to go 0-60 in 5 seconds just to get you to work everyday.