(simplicity of the map) alone is sufficient to judge a theory- you also need to take into account the theory’s parsimony (simplicity of the territory).
Solomonoff Induction gauges a theory’s parsimony via Kolmogorov complexity, which is a formalization of Occam’s razor. It’s not a naive measurement of simplicity.
The same observed that produced Copenhagen and de Broglie-Bohm produced MWI. You acknowledge as much when you state that Copenhagen extends MWI with more axioms. The observation string for MWI is then identical to Copenhagen, and there is no reason to select Copenhagen as preferred.