I think you’re equivocating on “mathematical formulation”. We want theories to predict the future. The algorithm that assigns probabilities to your future observations is the same, and equally mysterious, across all interpretations. MWI does raise the tantalizing possibility that the Born rule might not be part of basic physics—that it might somehow emerge from a universe without it—but AFAIK this isn’t settled yet.
I think you’re equivocating on “mathematical formulation”. We want theories to predict the future. The algorithm that assigns probabilities to your future observations is the same, and equally mysterious, across all interpretations. MWI does raise the tantalizing possibility that the Born rule might not be part of basic physics—that it might somehow emerge from a universe without it—but AFAIK this isn’t settled yet.