Wait, what about the part where everyone buys cheap Airbus planes and hedges them for when the price goes up? At some point, Airbus has to sell them for a profit, and it's at that point that people start selling
their stockpiles of cheaply-bought Airbus planes. They could sell it for anywhere between $1 and whatever the price Airbus will eventually want to charge, and still make a profit, while simultaneously taking away all profit from Airbus.
And in the above scenario, Boeing is also someone that could buy those cheap Airbus planes. I know, it's a contrived scenario, but I think it illustrates the point.
In the case of aluminium being subsidized by the Chinese government, same thing. The entire world, including America, get's to benefit from cheap Aluminium. You could argue it's a relatively direct subsidy by the Chinese government to all Aluminium consumers. The Chinese government, and their subsidized aluminium producers will not be getting that money back. And really, all they're essentially buying is a temporary halt on competition. As soon as they monopolize the market, and attempt to abuse it, competitors will start appearing and they're back to square one. With a large capital deficit and negligible profits from the exercise.
Alternatively, you get protectionism via tariffs. One could argue that that is a form of punishment on all the consumers of the tariff-ed good, or consumers of goods that are made from the tariff-ed material. The consumers pay more, and the government get's extra tax revenue. Does it buffer, and protect local industries from turbulent and cheap foreign markets? Sure, but that's at the cost of the consumers again. Really, the only winner is the state's coffer.