You said:

> Yes, it gets rid of the collapse postulate, but no, it actually introduces many worlds. [...] but in the end many worlds makes a metaphysical claim that two cats exist, [...] while Copenhagen claims only one cat exists in the end.

If you are saying that many worlds makes a greater number of claims than Copenhagen, that's incorrect, as explained above. The claims made by many worlds are a strict subset of Copenhagen.

If you are claiming that many words "introduces" the worlds but Copenhagen does not, that's also incorrect, because the worlds (it seems we agree) are also there in Copenhagen. If they weren't, there would be nothing to "collapse" in the first place!

If you're not saying one of those things, then I'm not sure what that paragraph is trying to say.

> But just because it is an additional postulate it does not per se make many worlds the better theory

It absolutely does, given that both agree equally well with observation.

Each additional assumption in a theory is an opportunity to be wrong. Therefore, given two theories which are in agreement with observation, the theory with fewer unchecked assumptions has a higher probability of being right.

A theory which disagrees with observation (like your altered relativity example) has zero percent chance of being right, so those kinds of examples aren't applicable.

This is just a somewhat more rigorous way of explaining why Occam's Razor is so effective.

For example, take [the dragon in Sagan's garage][1]. We have two models of reality: A garage containing (a) a dragon, who is (b) invisible, (c) dodges touch, (d) floats in air, (e) gives off no heat (f) etc, etc. Or we have a world/garage where none of those things are true.

Both models agree with observation— any measurement we make will not contradict either "empty garage" or "undetectable dragon". And yet one of them is a better theory. How do we know which one is which? The Undetectable Dragon Theory has far more unchecked assumptions (a...f) than the Empty Garage theory (everything in Undetectable Dragon, minus (a...f)).

Same thing for (forgive the extreme example) conspiracy theories. Moon landing hoaxers' ideas agree with observation— they just pile on a mountain of unchecked suppositions in order to avoid contradictions. If we're holding ourselves to good standards of belief, we pick the world model without all those extra unchecked assumptions. This becomes crucially important when there's disagreement about which theory is the Invisible Dragon theory.

Of course Copenhagen isn't nearly as bad as either of those, but the point is to call attention to the epistemological weight of each assumption we add, and what strategy we use for picking between two theories that are not (yet) contradicted by data. Copenhagen is doing more epistemological lifting, and so if we want to be good skeptics and efficient world model-builders, we should require its unchecked assumptions to be checked before we prefer it over other, more parsimonious theories which also agree with the data.

> which unfortunately adds much more personal preferences to the discussion

I quite disagree. The question is of "which strategy to use for picking models of reality which are most likely to be right". There are objectively good and bad strategies for doing that, in the same way that there are good and bad strategies for designing an airplane, or winning at chess, or proving a theorem. Of course no strategy guarantees success, and a "good" strategy might occasionally perform worse than a "bad" one— But without advance access to the solution, we don't know what those exceptions are, so our best bet is to go with the strategy which performs best a priori. In this case, for the sake of avoiding accidental belief in Dragons, the number of unchecked assumptions is centrally important!

[1] https://en.wikipedia.org/wiki/The_Demon-Haunted_World#Dragon...