Note that Hillaby has more “density” in the intervals with no gap between the first & second steps, where Robion does. Also note the much shorter recovery between intervals where 3.5 mins is harder compared to the longer 5 mins. That is all true, even though Robion has higher work percentage.
TR aims to make the Workout Level value look at and evaluate workouts based on the Work portion, but also the Recovery portion. Traditional measures like IF and TSS miss the recovery aspect since they don’t account for Work portions being combined, split, or spaced differently.
This is where the TR WL takes another step in helping identify the potential difficulty better than those older metrics.