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.
As long as Barcelona are leading by less than three points and until they meet Real Madrid head-to-head, bookmakers will continue to rate them as clear underdogs against Real Madrid (which are still priced at ~1.50 even after dropping points). The fact that they have 9 points is not bad, but you can’t say that they are winning confidently - three minimal victories and in every game they are conceding goals.