There is no one good way to assess any football player’s true value, whether that be over the course of a game, a season, or an entire career, and there never will be. There never will be. Value under these circumstances is an abstract concept with no clear answers on how to measure one player against another.
Is Aaron Donald more valuable than Van Jefferson? Objectively speaking, yes. That’s not in dispute.
But is Tutu Atwell more valuable than A.J. Jackson? Is Puka Nacua more valuable next season than Cooper Kupp? Did Janoris Jenkins have a more valuable career than James Laurinaitis?