Good points regarding Old School teaching and training curriculums. Such methods worked very well to weed out those who were unwilling or unable to withstand the rigors of 'eating bitter'. In my generation of students in our Shen Men Tao System, my teacher's son and me were the only ones who never quit, although he didn't really have the option of doing that, so we were regular training partners for all two person practices, and I couldn't have hoped for a better training partner.
One Old School teaching method, however, has unfortunately backfired to some degree. This was the teaching of more simplified versions of standard style forms for beginning and intermediate level students, which were easier for them to learn and perform until their overall strength, flexibility, balance, and body control developed sufficiently to enable them to perform the more advanced versions through ongoing corrections and refinements of the practice material.
Since there were no colored belt ranks to denote one's level of training experience, this could be easily identified by observing which variation of a form someone knew and how well they could perform it. Their bodies will tell more truth in 30 seconds than their mouths will in 30 minutes.
The unintended backfire often occurs because most students don't remain active long enough to learn the more advanced ways of practicing any of the form sets or drills, or long enough to learn all of the material included in a full transmission of the system. Nonetheless, many such individuals independently go out on their own and teach whatever they did learn to those who know less than they do.
This was and still is frequently typical in most CMA styles and systems. As a result, the vast majority of both live and video performances of the major IMA styles seen today reflect more elementary versions of what is being demonstrated, rather than the 'full meal deal' of the original forms and drills.
At the end of the day, it's virtually impossible to know or even realize what is missing from these simplified forms and drills if you have never been taught the more advanced, full fledged versions. Although I have seen many imaginatively creative attempts at reverse engineering various popular forms, none have even remotely succeeded due to the reasons mentioned earlier.
Thus, sadly, the Old School curriculums are gradually dying out as the very few who mastered them in any style grow old and die, oftentimes without finding any student who is willing and able to replicate the master's training regimen in order to achieve the same skill level.