But the wavefunction does have to collapse or decohere at some point because too large objects can not be in an entangeled superposition so if a macroscopic measuring device decoeheres and meauser a small quantum state that can collapse into 2 possible states the timeline of the universe either splits into 2 separete timelines that will not interact with each other because they are too different on the macro scale because of the measurement on the quantum nano scale. If the people that are using the measuring device to detect one of 2 possible states in the quantum state becomes entangled with the quantum state when they measure it the 2 different sates with the scientists can not interact with each other and will be separeted into 2 different timelines that will not interact with each other so if you believe that the wavefunction does not collapse it does either decohere in a deterministic maner and follows a skngle timeline or it separetes into 2 distinct and separeted timelines that will not interact and the wavefunction is not easier to calculate than classical macrosciopic physics in neither of these cases