IQ is not a perfect metric, but it is a decent predictor of many outcomes.
> the confounding factors of upbringing
This is why you do twin studies and studies using adoption as a control. We have quite a wealth of them. A good critical review of the evidence on both sides is here: https://humanvarietiesdotorg.files.wordpress.com/2013/05/the...
* Identical twins have a much higher correlation coefficient of intelligence than fraternal twins (table 5).
* Identical twins raised apart have a correlation coefficient for intelligence of around .73 (MZA studies).
* Correlation coefficients of IQs of biologically unrelated siblings raised in the same adoptive environment are approximately 0.
There are obvious confounds the paper mentions:
* Fraternal twins may not have identical environments.
* Adoptive environments may not represent typical parenting environments.
* Some of these studies have had poor controls and practices.
* Distribution of results from studies looks bimodal which indicates something weird is going on.
Still, even if you take the most critical view I think you have to accept that there is still substantial heritability of intelligence. These results cannot be convincingly explained any other way.
Given the difficulty of defining an objective measure for intelligence and the confounding factors of upbringing, I think it is almost impossible to find a good source on this sort of thing. Why should we go on a snipe hunt to prove your point?