There are two major things missing from a self-driven design education. First, going through a rigorously instituted design process which in turn helps develop and mature your criticality. The addendum mentions having a mentor which is useful even at the professional level. Where school differs is that you get strong, unequivocal critiques from people you may not always agree with, but these are often the most discerning and poignant criticisms. The design studios I learned the most from were always from the critics I most disagreed with, because they inherently challenge my preconceptions of ideas. The second things I see as a challenge is not participating in the design studio culture. In school you often learn from your peers, since you are all working on the same design prompt but have vastly different perspectives. It's such an engaging and energetic situation where you see the iteration and problem solving where someone is working on the same problem you are but has an entirely new approach.
These are some of my thoughts on formal design education, but I do think these ideas could be incorporated into an auto-didactic designer curriculum.
These are some of my thoughts on formal design education, but I do think these ideas could be incorporated into an auto-didactic designer curriculum.