Hi Paco,
I don't entirely agree that question banks are the origin of the problem, I would argue that it is in the exam questions; many are poorly phrased/translated, have multiple correct answers, are very often context dependent and sometimes just the examiner appears to be trying to show how clever he/she is.
From my own experience, I am well qualified in one of the subject fields (multiple degrees, 10 year research, teaching at postgrad level) to the point that I would be happy to call myself an expert (I also have a foreign CPL). I took a EASA practice exam cold and found to my embarrassment I could barely muster a pass! My downfall wasn't lack of knowledge (honest, guv!), it was the substandard questioning. With a bit of bank bashing I was able to get up to standard (frustratingly still not 100%!). The simple fact is with the current system, you cannot get the mark you deserve purely by knowing and fully understanding the subject matter.
Testing of a persons knowledge is always problematic, but there seems to be an obsession with the minutiae of the syllabus in the EASA exam system, which frightens/forces people into rote learning past question from the banks. If the exams were more focussed on the application of knowledge and principles we might actually enjoy the learning process, get an accurate gauge of the student's knowledge and even retain some of it beyond the exam room door.
G