The demon recoiled back, dodging Arad's relentless slashes. While slaps are easy to achieve due to the last surface area of the hand, slashes are much harder since they only hit with a line, and stabs are even more difficult to master.
When you hit with a flat hand, the attack angle doesn't matter as no matter how the attack lands, it'll always auto-correct into alignment with the targeted surface. Slashes on the other hand need a precise angle of attack; otherwise, the blade would twist upon contact and shatter due to the extreme stress.
Even though Arad's edge alignment was near perfect, it still led to his weapons shattering due to the added stress of the vibration of the blade. To be able to effectively do the slashes Kayden taught him, Arad must first understand the motions behind Dalla's slapping and use those to perfect his edge alignment beyond human capabilities.