Well, Kevin De Bruyne is a very important player in the midfield for Manchester City. It is nearly impossible to actually find a player like that. So of course when he is not there, Manchester City is going to find it really hard to manoeuvered the ball in the midfield area.
Does that mean Manchester City is useless right now? No absolutely not. But the freedom and authority that Manchester City had over the midfield in almost every match is not there right now without him. And without him, the supply for the forwards are also not going to be amazing, to be honest.
In fact, Manchester City is still performing well in the Champions League at the moment even without Kevin de Bruyne and managed to win the match against Leipzig, who are the strongest rivals in Group G, even though they have experienced 2 defeats in the Premier League this is really a shame, but I am sure Pep Guardiola wont only relying on Kevin de Bruyne, he still has several other key players, but we also don't know to what extent Manchester City will be able to survive without Kevin de Bruyne, but what is clear at the moment is that even though Manchester City has not appeared completely consistent, what is clear is that Pep Guardiola will soon fix things midfield at the club to be able to improve Manchester City current performance.