Many of us work the way you do, more or less of the time, and I think the fair term to use for that is fluency.

But I also think there are many working engineers, including some who have been in the trade for a very long time, that don't develop it.

There are surely other roads to doing good work without fluency, just like there is when forced to work in a foregin language with only modest proficiency, but I can't help but suspect it's a much more exhausting experience.