You could probably pick a honey yield figure to measure competency. No one route fits all sizes.
It is very difficult to quantify 'competency' in beekeeping. I think competency is set at varying levels and is commensurate with what a particular beekeeper wants from their beekeeping.
Some people will be happy to keep a couple of hives, be competent in what is required to keep a couple of colonies healthy, surviviving and producing a honey crop that their bees provide without undue manipulation. They may have no need for extensive knowledge of such things as bee morphology, queen rearing and microscophy and may have no interest in growing their colony numbers. They may be perfectly competent to manage the colonies they keep with a fairly low level of knowledge, managing within their level of competence..
I think competency often comes in to question when beekeepers move too fast for their existing level of experience .. escalating hive numbers, manipulating to increase colonies, rearing queens and seeking the elusive masssive honey crop .. without the necessary competence and sometimes without the desire or ability to gain the necessary level of knowledge.
I think JBM hit the nail on the head ..and the reality is that some beekeepers cannot recognise WHAT they are competent to do and as a result end up with problems that, with a little more knowledge in advance, could have been avoided. Whether that knowledge is gained via a mentor, beekeeping courses, reading, or the internet matters not - how people learn is a very personal attribute. I think, sometimes, beekeepers try to advance their beekeeping without seeking out knowledge in advance and without 'on the job' training ...something that would be frowned upon in any other 'industry' be it agricultural or otherwise.
This applies to both new beekeepers and those who have been keeping bees for many years ... extending beyond a competency level without the required knowledge is potentially disastrous on so many levels.