The Shadow Speed Technique used the Shadow Element as a pose to the Dark Shadow Element, as it was the most basic movement technique within the Shadow Steps Skill Book.
From what Damian had read in the Shadow Steps Skill Book, and comparing the Dark Shadow Energy, within the weird place he met the Shadow Kin King, to the Shadow Energy he felt in the area around him, he realised that it was inferior.
It seemed as though the Dark Shadow Element was unique and only accessible to the Shadow Kin race who had their own unique element that imbued both Dark Energy and Shadow Energy.
But Damian didn't let it discourage him, and began tapping into the Shadow Energy, that he sensed was found in all areas void of light, and planned to learn to wield the Shadow Energy to the best of his ability, before seeking out the superior Dark Shadow Element.