But you need to do a lot of speculative work before falsifiability becomes possible. And that speculative work is going to involve groping around in the dark being guided by mathematical logic (and a certain amount of politics, fashion, and wishful thinking.)
Considering physics as if MWI could be true has the potential to lead to mathematical elaboration and eventual falsifiability.
Considering physics as if there's no need to interpret QM because there's nothing to interpret (because Copenhagen is the correct interpretation) is a statement of faith, not rigour - because as a position, it's no more falsifiable than MWI, or Bohm, or any of the other interpretations.
The point of mathematical physics is to generate new falsifiable predictions. It's still science, it's just embryonic proto-knowledge - which is why it's called research, not teaching.
Considering physics as if MWI could be true has the potential to lead to mathematical elaboration and eventual falsifiability.
Considering physics as if there's no need to interpret QM because there's nothing to interpret (because Copenhagen is the correct interpretation) is a statement of faith, not rigour - because as a position, it's no more falsifiable than MWI, or Bohm, or any of the other interpretations.
The point of mathematical physics is to generate new falsifiable predictions. It's still science, it's just embryonic proto-knowledge - which is why it's called research, not teaching.