How does one know whether the weakness is in the art being studied or just in one's self?
A couple of responses come to mind.
1. Does it really matter? As long as the weakness is correctly identified and fixed, is it really important where and how it was done?
2. Honesty and Education. There will always be people that claim one art has all the answers. Investigate and explore those claims. Consider the amount of time needed to reach your individual goals and plan accordingly.