Yes, the idea of the “10x engineer” is essentially valid when you look at the contributions correctly (solving critical problems).
Back to your example, I have worked on difficult technical problems that were resolved after taking a break. Does that mean that all effort expended to that point was a waste of time? I take the opposite view, it was all that work that you expended earlier that allowed you to reach that point. Yes, you mind had to process that information, but it needed that information to process in the first place. Perhaps Edison already knew that intuitively when he said “Genius is one percent inspiration, ninety nine percent perspiration”.
It goes without saying that engineering is like any other field in the application of the Bell Curve (or Pareto if so inclined). Some (~20%) are going to be way more “productive”, as well as a few slackers (~20%). Most fall in the central peak.