That's why I said: "whether or not the DF21 can actually sink a carrier is irrelevant". Even if the DF21 had a decent targeting rate, there's no telling how effective it will be in actual combat.
However (!), that doesn't matter! The fact that the Chinese *could* have a weapon that can destroy a carrier poses a huge risk, not only to the US Navy and personelle, but to the image of American naval supremacy. No US administration is going to risk a carrier like this unless they were ready for open war.