From the remaining games, Karjakin-Giri was somewhat interesting, because Karjakin’s move looked like an error in transmission at first.

Is this better than 6. a4? Well, it doesn’t weaken the b4-square at least. If black answers with e6, then it can still transpose into the Qe1-Scheveningen. If black answers with e5, like in the game, then white will be able to either play Bc4 or Bg5 in one move, depending on what black chooses to prevent. In my opinion the critical move is 6…g6. There is no line in the Dragon where a3 really poses a threat.