There is indeed a lot to learn about the technical aspects of buildings - structure, fire requirements, M&E requirements, functional requirements, which are to be incorporated in a building. They are important but not what I would call the 'core subjects'. There are always the structural, M & E Engineers and other specialist consultants to fall back on in real life practice.

The core subjects are really design and construction (as in production drawings).  The latter is about knowledge of construction which can be learned and acquired through training and experience.  It's the design part that is elusive. It requires aptitude or flair, which cannot really be 'taught'. Some people have it, some people don't.  It can be nurtured up to certain extent (maybe 30%)  but to be able to excel, you really  need to be to be talented. Someone who is less artistic or creative would have a tough time surviving the architecture course.  Someone who is average in Art may be able to get through but they can only be a 'mediocre architect' in practice. That is why many of the architecture schools conduct interviews to screen the applicants.