Some dbz characters such as Majin Buu or Broly could be in tier 2 or 3. Majin Buu destryed a galaxy in the anime and though it wouldn't be immediate he would pose a threat to the universe in the long run.
Satsujinki(T.Shiki's more experienced version) would never be omnipotent. He shouldn't be an equal opponent against even a DAA(Dead Apostole Ancestor) in a fair fight.(it's other thing he strikes from the shadows, but still...not even near to a Vampire in physical powers). He's more like country-level in tiers...especially because T.Shiki's eyes far from being as advanced as Ryougi's. Ryougi Shiki(3) is another thing. She can kill even the whole world and reality. But Shiki(1) for example would be inferior to T.Shiki(while Ryougi's eyes are more advanced, T.Shiki physically much better). And Suzumiya Haruhi can recreate everything by just thinking about it subconciously. What else can be more omnipotent?
@Nerx: Yeah...one hit kill to the world for example:)...or killing such concepts like the distance between her and Syouren. And Ryougi(3) claimed she's able to recreate the whole world by killing parts of it. Satsujiinki on the other hand would die by frying his brain if he removes the holy cloth from his eyes for extended peroids. And only the dot-killing is a sure kill. with slashes T.Shiki can only kill simpler things and most probably Ryougi too, though it reverses with the activation of her 3rd personality(she's able to kill multipe things and cocepts by a single slash)