Kelvin is more important in the Manchester City squad than Haaland. Manchester City is used to build the strength of their squad around a midfielder rather a striker. If you check some seasons ago it was Yaya Toure who was the strength of the team and presently it is KDB who is the strength of the team. Manchester City has been scoring high amount of goals without Haaland. Haaland is just an additional striking strength.
True, midfield creativity in building attacks is very decisive in every game. Kevin De Bruyne is a very important figure for now in Pep Guardiola's squad. Halaand would not have been the top scorer if De Bruyne had not supported him, I think this cannot be denied.
Pep Guardiola himself admits that the injury suffered by his playmaker has had a huge impact on the Man City squad, the skills he has cannot be replaced by other players, such as Kovakic or Phil Foden.