Like I said, that's begging the question in the direction of materialism

Not at all. The question is only confused because the paradox confuses "knowing what would happen if neurons fire" and "having those neurons actually fire" as being the same sort of knowledge. In the human cognitive architecture, they aren't the same thing, but that doesn't mean there's any mysterious non-physical "qualia" involved. It's just that we have different neuronal firings for knowing and experiencing.

If you taboo enough words and expand enough definitions, the qualia question is reduced to "if Mary has mental-state-representing-knowledge-of-red, but does not have mental-state-representing-experience-of-red, then what new thing does she learn upon experiencing red?"

And of course the bloody obvious answer is, the mental state representing the experience of red. The question is idiotic because it basically assumes two fundamentally different things are the same, and then tries to turn the difference between them into something mysterious. It makes no more sense than saying, "if cubes are square, then why is a sphere round? some extra mysterious thing is happening!"

So, it's not begging the question for materialism, because it doesn't matter how complete Mary's state of knowledge about neurons is. The question itself is a simple confusion of definitions, like the classic tree-forest-sound question.