I think Jefferies well understood the requirements of designing a set for film or television, but he managed to design things that managed to transcend those limitations.
I couldn't agree more. His work was light-years (pun intended) ahead of the science fiction of the day and set a tone that still inspires to this day. Forget the details, the Enterprise in the JJ Abrams movies is Jefferies', as is every starship ever made for Trek that used the saucer & tubes design that he established.
The phaser, Klingon ship and more all reflect his outside-of-the-box thinking. Look at the Botany Bay – totally unlike anything else ever shown before, and even unlike his other ship designs.
I recently re-read the TOS Sketchbook which features lots of his sketches. He was in a league of his own. "Genius" is not an overstatement when it came to his work. Too bad he was never given an opportunity outside of Star Trek to create even more cool stuff.