Comment by Closi

Exactly this - people that understood the field well enough to add new knowledge to it has to be a pretty decent signal for a research-level engineer.

At the research level it’s not just about being smart enough, or being a good programmer, or even completely understanding the field - it’s also about having an intuitive understanding of the field where you can self pursue research directions that are novel enough and yield results. Hard to prove that without having done it before.