You can't get to the outside. No matter what perspective you are indirectly looking from, you are still ultimately looking from your own perspective. (True objectivity is an illusion - it amounts to you imagining you have stepped outside of yourself.) This means that, for any given phenomenon you observe, you are going to have to encode that phenomenon into your own internal modeling language first to understand it, and you will therefore perceive some lower bound on complexity for the expression of that phenomenon. But that complexity, while it seems intrinsic to the phenomenon, is in fact intrinsic to your relationship to the phenomenon, and your ability to encode it into your own internal modeling language. It's a magic trick played on us by our own cognitive limitations.

I think my objection stands regardless of whether there is one subjective reality or one objective reality. The important aspect of my objection is the "oneness", not the objectivity, I believe. Earlier, you said:

depending on which primitives and rules we have selected... Occam's razor will suggest different models... Minimizing complexity in each modeling language lends a different bias toward certain models and against other models, but those biases can be varied or even reversed by changing the language that was selected. There is consequently nothing mathematically special about simplicity that lends an increased probability of correctness to simpler models.

But since we are already, inevitably, embedded within a certain subjective modelling language, we are already committed to the strengths and weaknesses of that language. The further away from our primitives we get, the worse a compromise we end up making, since some of the ways in which we diverge from our primitives will be "wrong", making sacrifices that do not pay off. The best we can do is break even, therefore the walk away from our primitives that we take is a biasedly random one, and will drift towards worse results.

There might also be a sense in which the worst we can do is break even, but I'm pretty sure that way madness lies. Defining yourself to be correct doesn't count for correctness, in my book of arbitrary values. Less subjective argument for this view of values: Insofar as primitives are difficult to change, when you think you've changed a primitive it's somewhat likely that what you've actually done is increased your internal inconsistency (and coincidentally, thus violated the axioms of NFL).

Whether you call the primitives "objective" or "subjective" is besides the point. What's important is that they're there at all.