Only Barcelona have a perfect points so far (9 points from 3 matches), no one would be wrong to expect them to become La Liga champions this season, but that's too soon to say, we haven't even go to the first El Clasico of the season yet, so even though Barcelona are currently having a good run, we can't know how they will be after that.
About Barcelona's match against Rayo Vallecano, I thought Olmo played well, it's a shame he didn't play from the start, maybe if he played earlier we could have seen Barcelona's third and fourth goals.
Olmo came in as a super substitutions and he did well for the team. Playing and winning in your debut match should be something of great joy and encouragement for the player more and also for the team to have more trust on the player. Rayo Vallecano were not an easy opponent to beat but in the end they were able to record two goals against them that gave them victory. Barcelona cannot be predicted to be the La Liga champions just yet, they need to win more games and beaten even bigger team to make one feel so. They still have a long way to go but they’ve really started well in this manner.