> Educating doctors is really expensive. It would really suck to invest all that money in someone (or in yourself) just for them to fail a final test or whatever.

This happens already, today. There are dozens of reasonable questions you can raise based on this fact - but I don't think it's obvious that the failures at the end of training can majoritarily be identified by pre-training metrics.

Some countries allow any student to take the first two years of medical courses, and then impose restrictions on the following years. This seems a relatively fair system; you can imagine someone persevering over many years to attain the requisite knowledge - but this person would not have had the opportunity if there were a pre-medical school filter