It's true that the season has just begun, so it's quite natural to see the performance of the big teams has declined a bit... just look at how Barcelona at the beginning of this season was quite difficult to get more points, they were even held to a draw by Rayo, and also Atletico Madrid who is currently in a pretty bad condition, slumped to the bottom of the rankings due to not winning a single match.
These big teams are clearly having trouble organizing their game, but that doesn’t mean this will be the final picture of the season, usually big clubs have the capacity to bounce back and find their rhythm as the competition progresses. So I see these big teams coming back to the top once they get their game together.
I don't know, but as far as I know, performing well at the start of the season does not guarantee that a team will win the championship. The trophy belongs to the team that consistently improves its performance, not only at the start of the season, but throughout the season. However, on the other hand, when a team performs poorly at the start of the season, it gives a bad impression to its fans, making them doubt that the team they support can compete this season, especially when it comes to Atlético Madrid, who have performed poorly in their first three La Liga matches and have only managed to secure 2 points.
It certainly gives a bad impression for a big team to have a poor performance at the start of the season because fans certainly hope that they can at least show consistency and make a convincing start, but if their team's performance tends to decline, or even drops severely like what Atletico Madrid experienced, it will affect the fans and could add pressure to the team when their expectations are not met.
Hopefully, these teams can improve more quickly so they don’t lose momentum too early in the season.