New players occasionally take time to adjust and develop chemistry with teammates. Despite Al Nassr's success in the Arab Club Champions Cup, it's possible that the victory had a different dynamic than victories in domestic league games. Al Nassr and the rest of the team will face crucial challenges in their upcoming matches against Al Fateh and the AFC Champions League play-off against Shabab Al Ahli. They have the chance to show that they can overcome obstacles, adjust to shifting circumstances, and draw on their prior experience to do better in subsequent competitions. There are numerous variables that affect a game's outcome, so it's crucial to keep your attention on growth and learning.
I am guessing that it is going to take a few more games until they all adjust, plus the manager is a new one as well as far as I can remember, so even the players that used to be there last year will end up with some trouble. I think the fact that they won the cup is definitely a big deal, a big story to talk about, but looking at their current situation I would have to say they do not look like a good team at the league.
If it's a new game and new players, it's new season for other teams they lose to as well and they still managed to win. Adjustment period is true and they will play better that's true, but other teams had adjustment periods as well. Lets wait, if they are still not good a month later, then it's going to be horrible.