It's hard to compare theories that don't have well-developed mechanisms. If we're naive theorists comparing miasma vs tiny organisms, but you have no sense of how those organisms operate, its functionally just a comparison between one miasma and many miasmas, i.e. one vs. many nebulous non-mechanistic effects. In that case one miasma would be preferable. But that's not a demerit to the concept of minimizing entities as a theoretical virtue.

>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.