If that were actually true then we probably would be buying weapons from them. Why do you think other countries buy weapons from us?
They buy weapons from us because they cannot afford to RD their own. They buy from us because we are reasonably a reliable ally that will not cut their weapons off or attack them in the future. China is not a reliable ally, but a strategic competitor. Turning over all our steel manufacturing, rechargeable battery manufacturing, component electronics manufacturing, etc, etc, etc is bad enough. Just for your edification, this last war with Iraq the US literally ran out of ammo because we had only one factory that made military grade ammo. Luckily we brought from Taiwan and South Korea to make up for the temporary shortfalls. This is just fighting insurgents and getting National Guard units up to standard. Imagine if Iran decided to attack our stretched out forces in Iraq. Manufacturing is not just about the bottom line, it is also about strategic needs and contingencies. War is too important to be left to the politicians ...... and businessmen.