In fact, because Liverpool and their new coach make it impossible for them to compete fiercely with Manchester City.
Let's just look realistically at what is experienced by other teams, especially in the Premier League, that once there is a change of coach, the team will start from the beginning again and everything needs a process and time again, that is possible for Liverpool to happen so I don't think that they will surpass the strength/performance of Manchester City.
Manchester City is a pretty strong team now, in fact they are the strongest team in the Premier League, so don't compare it with teams that are currently building or want to develop.
If Pep Guardiola is still the coach of Manchester City then they will remain strong, regardless of whether they can defend the EPL title or not, they will still be at the top of the standings.
Now many sources are writing that this will be Guardiola’s last season in City, and I think that these may not only be rumors, he spent a lot of time in the team and may want to change something or move to another location. It’s interesting how Guardiola will comment on this, but I think we’ll find out somewhere closer to the end of the season, but for now he needs to think about becoming champions again.
As for Liverpool, I am also skeptical, because I expect that Slot, even if he does not want to change anything significantly in the team, he will manage the team differently, not like Klopp, and therefore the result will also be different. So I don't expect Liverpool to be a worthy competitor for City this season. Maybe Arteta will try to do this again with Arsenal if they manage to have a more or less stable season.
Talking about pep guardiola future, though their are already rumours in place that he may leave Manchester city at the end of the season, but it's still a rumour, and just as you rightfully said, the picture is going to be more clearer towards the end of this upcoming season, but if he eventually leaves Manchester city, it's definitely going to be a big blow to this Manchester city side, because you can't find a manager that is better than him right now.
Then as for Liverpool, to be sincere with you, I haven't seen how slot usually set's out his team, but what I actually knows is that the Liverpool I know under klopp will be very different compared to slots Liverpool, but would they be better? That's what we are actually going to find out next season.
Lastly, in my own point of view, right now the only team that I believe can challenge this Manchester city of this season title is arsenal, because if you take a look at the rest of the top teams, they aren't strong enough to maintain the high level of consistency to challenge the citizens, except arsenal, but I still feels like Manchester city will win it again come if care is not taken.