When you are dealing with traits determined by multiple genes that sort separately during reproduction, what you wind up with will be highly variable. That's why separate children from the same parents look different and often have very different personalities. Of course, as we've discussed, the 'nurture' aspect also plays a significant role.
There are no groups of people on the planet who are inherently smarter than others. That kind of thought process led to the myth of Aryan superiority that Hitler used as propaganda and that led to a world war and the deaths of millions - including millions of Jews in one of the most inhumane and hateful atrocities ever seen.
I think the expectation that all groups are absolutely equally intelligent, on average, is fiction on the level of the modern trans movement. The same goes for pretending that all families and individuals are absolutely equally intelligent.
I’d suggest those who can’t accept that have placed too much value on intellectual power—and with such misplaced emphasis have lost what is equal and precious in all.