A lot of uniques really seem to be balanced around the early/mid game, and fall off completely by the late game.
Some one them have some actually unique stat spike, like a very high crit rate or higher range, or in the case of guns, using a calibre that no craftable gun of that type can use (KH416 & MP6, N16, etc.).
But yes, only with expedition do we see the "out there" stuff, like the lemurian spear and sonocaster.