World ID explicitly set out to solve PoP, which includes uniqueness of individuals within a system, such that "creating 1,000 bot accounts would require finding 1,000 human users willing to consistently verify their authenticity"[0]. They consider CAPTCHAs to fail "because any human can pass multiple of them". They advertise it as a method for "Control Over Max Number of Accounts per Person"[1] (in addition to "Protection Against Unlawful Account Sharing").

So at the very least it seems like a core feature of World ID. For some other system, if it allows verifying users' humanness but not uniqueness or identity then I don't think I'd class it as an ID system. Maybe I'm failing to imagine all possibilities.

[0]: https://worldcoin.org/blog/engineering/humanness-in-the-age-...

[1]: https://worldcoin.org/world-id?for=apps