I taught in the UK before doing a stint as a 509 QFI in the US- working at one of the best flying schools in the country, which was a part of the largest civilian FTO in the world (no prizes for guessing which company!).
Even this large FTO had some serious gaps in training. For example, company policy banned landing on grass runways. This led to students being taught rough field ops by instructors who had never themselves done it for real, and who had in turn been taught by instructors who had never done it, and who had in turn....
Some of the US instructors trained for, and achieved, CAP509 approval: those who succeeded were excellent instructors, and completely belie any accusations that Yanks can't teach flying. However, they had considerably more inst. experience than some of their colleagues. As a contributor has said, the biggest problem (IMHO) with FAA instructors is that they don't need to be experienced to teach commercial courses, rather than PPL. Even to teach INSTRUCTORS, an FAA CFI only needs to have done 200 hours instructing!
And that leads us to a problem. Under JAA, the instructional experience of FIs is much less than that for 509. At the same time, the course is shorter! On balance, I prefer the CAA syllabus, and the level of standardisation required of 509 schools.
Again IMHO, the US system works for the US because their airlines use the commuters to weed out those unsuitable for larger aircraft. In the UK, and in much of Europe, we do not have anything like the number of commuter companies. Population densities are such that the distance which might support a Beech 1900 in many parts of the US, will support a 737 (or at least an ERJ145). Therefore, the weeding out has to be done in the training process. Hence, UK licences, and many other European licences, were a real pain to obtain. The good US schools are aware of this: the mediocre ones put out a US product (possibly a good product, but for the wrong market) for a European requirement. The bad schools: just don't go there.
Room for any more in the bunker?