>i don't agree that 'count of entities' is the correct criterion for what makes a theory more or less parsimonious/occam's razor preferred.
I mean, its literally in the original formulation of Occam's razor: "plurality should not be posited without necessity". But there are many ways to justify this. My preferred argument is that fewer entities means fewer resources with which to "bake in" the explananda into the theory. The more knobs to turn to generate your empirically adequate theory, the less likely your theory will capture reality.
>[Copenhagen] just proposes that it collapses when measured by the apparatus
Measurement isn't limited to an "apparatus". Collapse of superposition is a feature of large scale interactions. While there is branching, in practice it is bounded because interactions tend to cause collapse.
"sure, we can observe bacteria and viruses in the lab individually - but when we move to the physical world disease spread is described by miasma which is simpler and thus this is the more parsimonious theory." there are fewer entities in miasma - but you still have to posit this additional thing (the miasma) on top of the already observed viruses and bacteria.
similarly, i don't agree that 'count of entities' is the correct criterion for what makes a theory more or less parsimonious/occam's razor preferred. it is about the number of rules even if there is a single rule that creates exponential entities. Copenhagen would also predict this 'exponential branching' in the system under observation - it just proposes that it collapses when measured by the apparatus: an additional rule that makes it less parsimonious than many worlds