Proof-of-work was created precisely to prevent a Sybil attack, but while allowing an open network (i.e. not having to buy the token from the creators). You nee

Proof-of-work was created precisely to prevent a Sybil attack, but while allowing an open network (i.e. not having to buy the token from the creators). You need a form of scarcity to prevent a Sybil attack. Solved cryptographic puzzles of an adjustable difficulty is one such form of scarcity. Does this address your concern about relevance?