Has value discovery already mostly happened in ETFs?

I've read a recent comment here on WSO about how the stocks of companies in the SP500 have most of the value already discovered prior to being added to the index. If this assertion is true, would this imply that the face-value returns of the SP500 are misrepresented (so the actual annual return less than 11.1%) since people who buy them now wouldn't get the same degree of price appreciation as previously?