I think part of what he's insanely good at is carefully soliciting feedback from other people, particularly those with a lot of experience with similar but distinct problems. The final spec goes back close to a year (https://www.aeracode.org/2015/6/17/beyond-request-response/ https://groups.google.com/d/topic/django-developers/mt1mTNvc...) and the polish really shows.

I think of that as a “senior developer” skill which is easy to underestimate since it doesn't directly translate into tons of commits but is so critical to the long-term success of a project.