Time and Life weren't elements in the same way that fire and ice were elements. They were more conceptual and Toa couldn’t control them. They were referred to as "Legendary Elements".
Elements were generally distinguished from other powers by having Toa with their abilities.
The Ignika and Vahi were on the same power level because the elements they represented were codependent.
The only special thing about the six "standard" elements was that Matoran of those elements lived in Metru Nui.
- Greg Farshtey saw Toa as being avatars of the fundamental forces of the universe. Powers like stasis field, elasticity, and the like were not fundamental forces, but more like superpowers. He saw them as the type of power a mask would have rather than a Toa element.