Dani Olmo's arrival is pretty good, Barca has strengthened the team. Olmo is a player who will be worth the big money paid. When he came to La Liga after the Bundesliga, it's admirable that he adapted instantly.
It's interesting that Barca won all three games same score, 2-1. In two of them they came from behind to turn the game around. I think all these oppontets were medium difficulty and it's good that they got through them without any point loss. Other contenders lost points and Barca are on top. They have more variety in attack this season and they can get Lewandowski more of the ball. The wings are working. I think they have everything to be hopeful for the title.
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.
Barcelona were very impressive with the results in all the matches played but not with the performance. So far, all the the three games played were so terrible especially in the first half including the yesterday game. They should better work on it else tough opponent will make use of that opportunity and they will not be able to turn things around in the second half as usual. Did you also notice that they haven't kept a clean sheet in any of the three matches played? It tells how bad and porous the defense is. It's worthy of notice how impressive Olmo is with the performance he's displaying. He deserves a starting spot in the squad because of his creativity.