The tonnage of Chinese nukes is 294 MT vs. the US's 570 MT.
NTI: United States - Nuclear Disarmament
NTI: China - Nuclear Disarmament
We have fewer missiles, true.
But we have missiles that have multiple megatons on them rather than the US's hundreds of kilotons.
If the US tries, it would be about 1 missile needed to take out 1 major US city vs. 4-5 needed for each Chinese city. 294 megatons, assuming 2 megatons per city needed to kill 90% of the population, can easily vaporize 200 million Americans directly, destroy 99% of US industry, kill the rest with slow radiation and permanently end the US as a nation state. The US isn't going to risk that.