Exams are, in my opinion, a poor way of evaluating a persons level of knowledge and understanding. If it was common place to answer exam like questions in the work place under exam like conditions, it would be highly relevant to use current exams as a method to evaluate people, however, seeing as you don't need to know everything at any one time and you will mostly be able to check other sources, exams don't really give a fair "every day" evaluation.

I don't know what should replace them, but I don't think they are fair.

The old O levels did give that snapshot. They showed what the person was able to do in a high pressure environment. All with the same starting position. Coursework can change that. You may or may not have access to data and as such can possibly do better than you would in normal conditions.