-> She's a historian, others aren't.
-> Her life's mission has been to uncover the history of 800 years ago, others' isn't.
-> She's "light of the revolution", others aren't.
-> She carries the will of Ohara, a nation who's scholars took a stand against the World Government and got wiped off the map, others don't.
-> She's researched various poneglyphs even before joining the strawhats, others haven't.
What makes Robin special isn't simply her ability to read some ancient language that no one else can. That's still part of it, as she's only 1 of the 2 people in the world who know the language, if being 1 of the two of however billions there are in the OP-verse makes her not unique.... then idk what to say my guy, other than your expectations on being unique are simply too high.