Passing a training course at the Airservices College does not necessarily mean that you are good enough to do the job. All it means is that you are good enough to try to do the job.
I don't know that statistics but if you think it's all over after the ATC college you're kidding yourself. On my course (many years ago) that actually passed the college there were plenty of people who were so confident of their ability....50% didn't check out.
I'm sure AsA has got their training programs much much better nowadays - those bank managers would have made sure of that. The instuctors at the ATC college these days are definately some very experienced people but that doesn't mean they can fully prepare you for the reality of doing the job. Standards are necessarily high - some people can't make it - some people do who shouldn't (maybe a couple of managers in there) - some have a natural ability.
There are a couple of old guys who are your instructors at the college who can give you some no BS advice on what you need to do. Listen to them.