In the US, we already know from numerous surveys that after the first graduate intake, most software hires are made by personal recommendation - which is obviously going to exclude anyone who isn't part of a network.
So those are two examples of the value of networks.
As for "grit" - what does the word even mean? If someone gambles everything in startups and loses everything three times in a row before giving up, do they have grit or not?
So obviously grit isn't the unifying thing that leads to success.
High Schools and Universities are by no metrics a measurement for success. And if you want to make them that you can start with the luck of whether you are born with rich parents or poor parents.
Of course grit is good to have, but it's not what define success.
For example, imagine we assign 'grit' ratings to students who finish high school. Later we find that students with high grit scores tend to complete a university degree much more often than those with low grit scores. Would that change your mind about the importance of grit?