Meldrew of Meldreth wrote:
writes
By the time they've reached 18, it is easy to see that a significant
number wouldn't benefit from University. (Other forms of further
education or vocational training, perhaps; not University).

But wouldn't they be better at determining whether or not they benefit?

Who is "they"? The University admissions process, or the potential
students?

The potential students. The University admissions process is not capable
of doing that, and nor could it be made capable at a reasonable cost (if
at all).

How does ease of determining how deserving they are alter the original
proposition?

Which proposition did you consider to be original?

Potential students should always get the opportunity, whether or not
anyone else considers them deserving of it. If the admissions process
(assuming it's not as unfair as it was a few years ago) prevents them
doing the courses they want, so be it, but economic factors should not.