But people usually aren't talking about intelligence. They're talking about success in life, be it career or school.
Our oldest old had a terrible time at math, and the teacher thought she was doing well in the start because she never asked questions.
But the first practice test showed otherwise. After that we made a point to ensure she understands math. It was a rough couple of months at the start of the year, but that's paid dividends and the last 5 have been pretty smooth.
She didn't get smarter. And if she didn't have parents with the time and ability to help her, she woulda flunked.
The effort at home involved gentle encouragement and keeping him focused on the phonics homework. It wasn’t tough on him or us but it has restored his confidence and he’s keeping up with his classmates now.
This is totally the kind of problem that could have festered and led to poor outcomes for him in all of his schooling if we’d ignored it.
I do believe parentage changes "the difficulty level" of life. Some kids are born to loving, nurturing, well-off parents and essentially "play the game of life" on level easy. Some kids play on level hard. However, it's the kid's own choice how they will play it.
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.
I'm believe that beyond a base level of food, clean clothes and love, your influence as a parent is marginal. It's also a wildly unpopular but intelligence is highly genetic (at least 50% of outcome determined by genes).