It's kinda evident in this debate as well to an extent. It's what the Greek poet Archilochus called the Fox and the Hedgehog. Basically suggests that the Hedgehog knows one thing, and tries to shoehorn everything into that one lens. The Fox is more diverse and accepts that things are complex.
So in this instance, the hedgehog thinks that social mobility is low because the system is rigged (innit), whereas the fox thinks social mobility is low because of a multitude of factors that make easy catchlines difficult. In essence, if you can boil an issue down to a newspaper headline then you're almost certainly looking at it too narrowly.
For instance, if you look at success in life, you have to consider things like the work ethic of the individual, the connections they may have, their personality and social skills, their gender, the companies they work for, even things such as whether they start their careers in a recession and no doubt many other things. Just boiling success or failure down to the wealth of your family is far too simplistic imo.