I genuinely don't understand the point in contention here. I get the positive manifold, which is a thing out there in the world. I get that it is a positive manifold across tests that it might be argued have an ambiguous relationship with what we subjectively call intelligence.
Causality is the point of contention. g has no referent which could be studied via causal modelign. Even weaker in fact, there is no physical phenomenology. There is no part of the brain you can point to and say, "this is the g part of the brain" afaict. Phlogiston comp is apt.
So the point I don't get - presumably because I don't have a deep enough understanding of the relevant stats - is why anyone cares if 'g' is a genuine thing vs. cognitive ability being a bunch of abilities that are correlated.
This seems, to me, to be completely irrelevant to the core question of whether those cognitive abilities are mostly innate or whether they're driven by environmental factors.
It's *interesting* that a lot of what we've decided are valuable cognitive abilities are in fact correlated, but it's not clear to me why this fact has so much significance in debates around IQ and heritability.
If you set aside social superiority motivations, there is something curiously arbitrary about studying intelligence this way at all. It's like if Kepler had taken Tycho Brahe's data and tried to correlate them to astrological predictions instead of to simpler orbit geometries.