This is very true and I agree with the core points. I also think that there is more to be said for the skills/advantages that aren't easily quantifiable (e.g., habits passed down from parents, mentors, etc) and have a tremendous impact on upward mobility. Those habits are usually reinforced by the culture and if you are unlucky—more unlucky than just being born poor—then that can have an even larger impact on your odds (think of people who are born black, poor, with one parent, and in certain areas in the US).

I am not an expert but I do expect the epigenetics field of study to help us build a better understanding of the things touched on in this paper.

P.S. you do have a "point". Someone saying that you don't is a cop-out so they don't have to think about how to engage in a conversation, debate, or discourse.