This is an interesting statement to me, and I think the truth of it is debatable. It's certainly true if you're only looking at a specific sort of player experience, but there are other sorts of experiences some people want which is greatly enhanced by the use of reference material.
Why would a game designer want to reduce the appeal of their game to those sorts of players? Players who want the "pure" game experience can simply not look things up on the wiki.
Surely, in the end, game designers want to make games that are fun and engaging, so if the use of a wiki makes a game more fun and engaging to some, why would a game designer object to that?