Alan Kay said "A change in perspective is worth 80 IQ points,". A change in perspective is often brought about by communication or I/O. In my experience this often bears out. The people who communicate get more done than the clever person who doesn't get out into the problem domain. The limit is I/O not intelligence.

In my work, I have always found that the main "blocker" (I hesitate to use the term "bottleneck"), is human nature.

If we design stuff to be used by humans (what I generally do), then it's imperative to take basic human nature into account, and that can be incredibly annoying.

Annoying, or not, human nature is a major factor, and won't go away, no matter how many times we tap our heels together. I think it was Philip K. Dick that said "Reality is that which, when you stop believing in it, doesn’t go away."

Designing stuff for processes and machines to consume, is pretty straightforward. Designing stuff for humans, however, is really challenging (which is one of the reasons that I like doing it).