Every team usually have their peak season and this season is definitely not the one for Manchester City. Even if they eventually win the premiership title this season, there is no basis for comparing the Manchester City of last season to the one we have now.
Manchester City performance dropped dramatically this season, we can’t compare their performance this season with last season, they played better last season compare to how they played this season. If you notice how Manchester City have been playing since being of the season, you will notice their is a drastic decline in their performance, their was a certain time that Manchester City were finding it very difficult to score goals in their matches, they were always having opportunities to score but they were missing it, most of the matches which they won then was just with one goal difference.
Am still expecting Manchester City to win the league this season, but that doesn’t mean they are really in form just as you said, their performance this season can’t be compared to last season. Maybe De Bruyne that has always been on injury has really contributed to decline in Manchester City performance this season.