This is all so very 1980s. Fusion and fission weapons are nice to have and all but we live in an era where just the threat of chem and bio weapons can collapse entire nations into chaos. It is not an impossibility to use covert and commercially convenient means to deliver the components of such weapons into every corner of the populated world in case of MAD. Of course their existence remains a question but is it really such an impossible task? China's certainly not the first or only competent player in these fields.
Total annihilation of global population in case of retaliation can be achieved in plenty of ways. Nuclear is just the fireworks everyone's still enamored by. Spending "too much" on ICBM and warheads maintenance can be cost inefficient for what the tools offer if better tools exist. More than 1000 high yield warheads is for the insecure man and is really betting on and safeguarding against a world nobody wants. Better those funds go into hypersonic delivery procurement and research to improve existing systems. As for the warheads themselves, 200-300 even if true is enough to supplement the masses of bio and chem weapons. Spend a few billion buying those Russian nuclear powered cruise missiles and torpedoes once they perfect them too
There's also no immediate threat of full scale nuclear armegeddon yet anyway. If there was, there's no barrier to China really going Russian/US crazy in numbers except for maybe nuclear material. Enrichment technology and rates are no problem. Not missile building or delivery systems. Not warhead miniaturization or delivery. If material is truly a bottleneck, it makes more sense to have quality in the material and delivery systems that are developed and fielded.