I have not read the book, but I see a mix of intuitive and slightly dodgy reasoning here.
As someone who talks with an extremely wide spread of students, I see the 'drift' term big time. There's listless drift, as in low motivation and "powered drift" where students work hard, but their motivation is essentially "my parents made me do this".
People who do "business" degrees are selected from the set of people who lack enthusiasm. Anyone who actively wants to be an accountant at 16 when one enters the degree decision system, has in my opinion something really wrong with them. Social work attracts people who can't think well so it's hard to make them better, ditto 'communications'.
The reasoning of the author is however questionable, since he says in effect, "people who do degrees where you write essays get better at writing essays".
Also "complex reasoning" begs many questions.
I'd bet real money that the tests taken had a liberal arts bias, in that they assumed simple two valued systems. Ironically arts are more boolean than CompSci where one must elicit values from uncountable systems.
LA's are trained very hard to see the world as dialectic, two sides to everything. You can make many of them really quite angry by careful use of Aristotlean three value logic, and the idea of the right answer being a curve can induce symptoms akin to physical pain.
