Well if very few active first officers or captains can pass the ATPL(A) theory if they were given the task again without long refreshing work then the exams are clearly not good enough because they ask about stuff that is not practically useful. So there should be a total revision of the examinations and the theoretical examination should probably be done in an oral form for example in a simulator with real life topics. Then people would actually learn the useful theory and not learn how to answer questions with 4 answers.
But it would probably cost a lot to create such oral examination system even if the students were to pay the salary to the examiners by exam fee. So EASA just continue to use what they got and hope the students will learn the practically useful knowledge from their instructors, be examined from it by the practical examiner and learn the rest at MCC/JOC or APS MCC + at the type rating and line training.