Well Man City remains a strong team. In fact, there are actually no major changes in the composition of the Man City squad this season compared to last season. So I don't think Man City's performance will decrease. And it could actually have increased. Gundogan had indeed left. But many other midfielders can replace his position. Although not as good as Gundogan, Man City still has very high quality players compared to players owned by other teams.
A lot more great players left last off-season and I remember how they tried to reproach Guardeola with this when Arsenal were in the lead in the Premier League, but according to the results we saw, in the end City won all the most important tournaments. This time, the championship squad remained, so this gives Guardiola an excellent chance to continue to win. For Arteta this season, in addition to the Premier League, they will have to play in the Champions League, which will significantly add to the burden on the team.