The heredity of intelligence actually depends on the environment. Those high percentages you mention only emerge in a 'stable' environment. That's not saying that people can grow (far) beyond their genetic makeup, but the opposite can happen.

If you think of (defending against) all those negative effects, I think the impact of a parent goes well beyond the basics you mention. That goes even further when you consider all other skills that one can foster that benefit a future member of our society.