I think some cases cases of what you’re describing as derivation-time penalties may really be can-you-derive-that-at-all penalties. E.g., with MWI and no Born rule assumed, it doesn’t seem that there is any way to derive it. I would still expect a “correct” interpretation of QM to be essentially MWI-like, but I still think it’s correct to penalize MWI-w/o-Born-assumption, not for the complexity of deriving the Born rule, but for the fact that it doesn’t seem to be possible at all. Similarly with attempts to eliminate time, or its distinction from space, from physics; it seems like it simply shouldn’t be possible in such a case to get something like Lorentz invariance.
I think some cases cases of what you’re describing as derivation-time penalties may really be can-you-derive-that-at-all penalties. E.g., with MWI and no Born rule assumed, it doesn’t seem that there is any way to derive it. I would still expect a “correct” interpretation of QM to be essentially MWI-like, but I still think it’s correct to penalize MWI-w/o-Born-assumption, not for the complexity of deriving the Born rule, but for the fact that it doesn’t seem to be possible at all. Similarly with attempts to eliminate time, or its distinction from space, from physics; it seems like it simply shouldn’t be possible in such a case to get something like Lorentz invariance.