Oxford may be different to other Universities. LSE is stuffed full of students, a bit like OPs son, who decide they want to go into IB then work backwards.
Many of them seem to work very hard indeed to land first an internship and then a job. Lots of networking breakfasts, appointments with the careers office, plenty of multi stage applications, careful selection of courses to make sure you land the first.
It may be they have to try harder because they are not Oxbridge. But certainly plenty are meticulous, and high aspirations seemed part of the LSE culture.
I think it is an advantage to experience IB, law or whatever high powered career ypu are aiming for even if it involves pulling strings. Not to get the job, but to gain an idea of whether this is what you really want to do with your life. One friend of DS' landed a spring internship with Goldman Sachs, which led to an offer of a full, and amazingly well paid, summer one. Unfortunately the couple of weeks convinced them that IB was the last thing they wanted to do, and they would prefer focus on getting a job in the public sector.
I dont know if it is still the case but firms like JP Morgan based in Bournemouth/Poole were offering work experience to local school children in conjunction with Bournemouth Uni. I assume similar happens elsewhere. Firms want to ensure they have the pick of the local workforce, and probably want to ensure they reflect local diversity.
But its like many MN discussions. There is an assumption that all DC are super high powered. But actually in real life people fall into things for all sorts of reasons. Some obviously will have been on a golden track through grammar/private school, Oxbridge and grad scheme. But as time goes on they will find plenty of peers who have different backgrounds.