Basically Arsenal is still the same as Arsenal last season. They are strong and quite consistent, but they sometimes lose that consistency at times which makes Arsenal always fail to maintain the top position. In that match I also felt surprised. Not because Arsenal won, but I was surprised by the score resulting from that match. The 5-1 score is really an indication that Manchester City's strength level this season has indeed decreased quite significantly. So Manchester City's level of strength which can usually fight fiercely when facing Arsenal is now no longer visible. I might be happy with Arsenal's win because I also favored Arsenal to win. It's just that I still wonder how Manchester City could become like this in a short time. This drastic decline was truly a big surprise this season.
Arsenal aren't perfect either, they just did everything right in this game. And until the 56th minute, when City started to lose 2-1, the game was quite even and I can't say that City were so bad up until then that they lost like that. In the last half hour of the game, their defense fell apart, they gave the ball away to Arsenal too often, and against such an opponent it's a very bad idea and as a result they conceded a few more goals.
Manchester City team was not strong for attack even when they equalize 1:1 by E. Haaland, their was no force to launch an attack to defeat Arsenal even though they equalise, secondly, you said it here, their defensive player later became weak that gives Arsenal's more edges to penetrate to their goal post, so I think Manchester City problem of giving Arsenal bags of goals, is as result of their the formation they used, and the strength of their defenders were exhausted.