In your scenario, despite the unrealistic coding process, the machine code is the source code, because that's what everyone is working on.
In the development of LLM, the weights is in no way the preferred form of development. Programmers don't work on weights. They work on data, infrastructure, the model, the code for training, etc. The point of machine learning is not to work on weights.
Unless you anthropomorphize optimizers, in which case the weights are indeed the preferred form of editing, but I had never seen anyone---even the most forward AGI supportors---argue that optimziers are intelligent agents.
