Nathan, thanks for reading.
I would be curious if Germany's coal is balancing all of its wind. In general, Germany is a difficult comparison to make for China, because it is effectively balancing over all of Europe. The same logic also applies to Denmark, which can accommodate 50%+ of wind without significant curtailment.
Also, vis-a-vis marginal costs: renewables have marginal costs of effectively zero (it costs the same amount to keep the turbines spinning as to feather or stop them). So once they're built (e.g., with the help of subsidies), the market should accept as much of this free resource as it can. Hence, a true wholesale market -- lacking in China -- does help to push the limits of coal plants. By how much is unclear.