I still don't know why people are already expecting too much from these teams already. They league just started and they have all played only one game in the league phase, remaining 37 matches which is still a long time from now. But the this, we are all doing prediction and these predictions are based on the level of signings the teams made during the transfer window.
The problem is that we expected the team's performance based on the huge amount of money they spent on recruiting players during the transfer window. People believe players who have been signed for more than €50 million to perform well in the first match of the season. Before the season, Chelsea fans expected João Pedro to be the best striker and Jackson to leave the club this summer. But after the game against Crystal Palace, some fans believe Jackson should stay.
However, I agree with you that there are still games to play, this is just the start of the season, and we never know what the future weeks will bring. The guys that Manchester United signed performed well in their first game, and Gyokeres had zero shots on target against a team he rejected, I wouldn't say he played badly because Arsena overall performance in the first game was poor.