Last season, Man City experienced a slight decline in performance because De Bruyne was injured and Haaland was also injured. And last season Gundogan also went to Barcelona. So Man City also fell behind in the EPL. But since De Bruyne recovered and played games, Man City returned to better condition and continued to collect points so they were able to catch up with Arsenal, who were at the top at that time.
Haaland was controlled better by opponents in Premier League and it was not only because of his injuries last season. With De Bruyne, he will have less contributions for Manchester City with time when he gets older and his body will be affected negatively. De Bruyne is helpful for Manchester City in some matches and if he is used properly but he won't be able to play all matches and fulfill each match like when he was younger some years ago.
If Manchester City rely on contributions from Haaland and De Bruyne, they will have big troubles this season and in future. If they come to that day, Pep Guardiola will make his clever decision to leave Manchester City and find a new challenge, new chapter for his coach career.