Can't speak of CPL/ATPL stuff as I've never seen them,
Historically, the commercial exams had two sources, the Air Registration Board for Technical Exams and The RAF for Nav Exams, produced until 1974 by the College of Air Warfare. This was the origin of the two exam groups which the CAA took over in 1974. The material remained largely unaltered, except for the addition of new material and the removal of some questions that were grossly out of date. The quality of these questions was questioinable and with the advent of the JAA and a European Database, there was an opportunity to produce an examination system that was fit for purpose however; the process adopted lead to an even greater reduction in relevance and quality. With no requirement to write new questions, the CAA disposed of its Ground Examiners, with the result that there was nobody left responsible for PPL exams, which did not fall within the European remit and for the past 20 years has been a secondary, unfunded task.
In the entire history of aviation, there has never been a training analysis to determine what a pilot needs to know; consequently, the examination system has never had any meaningful purpose.
I was involved with the initial vetting of EASA ATPL exam questions designed to replace the JAA database, but again not at PPL level. The quality of these new questions was the lowest I have ever encountered; fortunately, they ran out of money and the project was abandoned.
The BMAA were quick to grasp the nettle, they wrote their own exams, gave them to the CAA who were happy to adopt them. The CAA are not funded to produce PPL exams, so there is an opportunity for industry to present them with a working solution, which I am sure they would be happy to adopt.