Since the Justifier set has the same bonus (Handgun speed increase: Medium) as the Nameless set, it should possibly get Movement speed increase: Low each piece in order to differentiate it from Nameless.
My reasoning for this is due to the fact that the Justifier Jacket's description is "A finely-made suit for danger-seeking gunslingers who would much rather be quick than dead."
Quick as in quick drawing their guns. They are gunslingers, not runners.
Nameless has different defense types, much like skolver and snarbolax sets.
There's nothing wrong with the premise (could be a gun equivalent to mercurial demo). But there aren't any serious reasons to change justifier either.
You could just suggest a new gunslinger upgrade path.