There was a very concrete example of this. In his previous mission at Mt Zurtun, he had run into a powerful defensive Martial Artist who could entirely negate the entirety of Rui's offensive arsenal. He had, to some degree, turned into the motivation and inspiration for Project Bounce.
The man's defensive prowess came from techniques that were synergetic enough with his rubberized Martial body. Together, his defensive prowess was far greater than that of an all-rounder Martial Squire like Rui, than it would have been had both of them been Martial Apprentices.
Yet, now that Rui had created the Flux Earther technique, he didn't think there was a significant gap between their defensive prowess at all. Rui was very confident that the Flux Earther technique could replicate all of the feats that the defensive Martial Squire had accomplished in their fight.