And it should be noted that parents do have control over peer group: where to live, public school vs. private school vs. homeschooling, getting children to join things, etc.

Exactly! If you have something to protect as a parent, then after hearing "parents are unimportant, the important stuff is some non-genetic X" the obvious reaction is: "Okay, so how can I influence X?" (Instead of saying: "Okay, then it's not my fault, whatever.")

For example, if I want my children to be non-smokers, and I learn that whether I am smoking or not has much smaller impact than whether my children's friends are smoking... the obvious next question is: What can I do to increase the probability that my children's friends will be non-smokers? There are many indirect methods like choosing the place to live, choosing the school, choosing free-time activities, etc. I would just like to have more data on what smoking correlates with; where should I send my children and where should I prevent them from going, so that even if they "naturally" pick their peer group in that place, they will more likely pick non-smokers. (Replace non-smoking with whatever is your parenting goal.)

Shortly, when I read "parenting" in a study, I mentally translate it as: "what an average, non-strategic parent does". That's not the same as: "what a parent could do".