Best player doesn't equal biggest blow to the team if they become unavailable.
If Ozil gets injured, Cazorla is capable of taking his place. If Sanchez gets injured, we could cope by having Walcott on one wing and Welbeck on the other. What we wouldn't cope well with is Giroud getting injured or Kosc getting injured (although I would put both in our top 5 players quite comfortably)