A lot of those studies work very hard to split apart the genetic (and sometimes including epigenetic) factors at point of sperm meets egg, the environmental factors in the womb, the parenting factors, and/or the rest of the post-birth environment. They're not doing a simple ratio.
And to the extent that research successfully isolates the genetic factors, we know it's not some outside factor causing a correlation, and we know it's not IQ causing genes. Anything isolated there is genes causing IQ.
