The ATPL exams are highly specific, require little or no understanding, and in many cases actually promote incorrect answers to the questions they ask. In essence, they are an exercise in rote learning which can largely be dispensed with as soon as the exams are passed. In terms of their equivalency to other examinations, I'd put the 14 exams as equal to 3 or 4 GCSEs and no higher. The amount of study required is fairly irrelevant - all exams require large periods of study.
ATPLs are just one, relatively small, hurdle on the course to becoming a commercial pilot.
Scroggs