Too much structure and an art can be become rigid; physically and mentally.
Too little guidance and framework, and the art can fold in on itself.
Tai chi classes in the 20th Century fell prey to bad teaching standards, little or no syllabus, no testing of skills, and low standards.
Unfortunately, internal teaching methods vary from school to school, with each instructor essential teaching as they see fit.
This can be good sometimes.
It can also mean sporadic progress, if any.
Whilst a Japanese martial arts teaching approach does not quite fit the internal arts, it does offer some valuable lessons in terms of consistency and continuity.