Studies done with adopted children appear to show that slightly less than 50% of intelligence is heritable[1]. That means that a good deal of it isn't, but to say practically undetermined seems like an exaggeration?
I'm replying to myself because re-reading this comment is sounds a little callus. While I am implying that we can't say for sure what fair looks like given human variation, we also can't say that the current distribution is fair the way basketball appears to be.
[1] https://www.sciencedirect.com/science/article/abs/pii/S01602...