Nowadays, the Izumo would be instantly perforated by China's supersonic cruise missiles and "DF21-ed" to hell the moment any shooting war breaks out. JMSDF ASW assets are pretty dangerous to China's submarine force and hence priority targets warranting even ballistic missile strikes.
A totally unproven, over-hyped, system. The shooting of which would automatically trigger the Defense treaty with America and give the Chinese a much bigger head ache. One flat top would instantly become about 25 flat tops to worry about. Also Japan herself has a very capable submarine force and the PLAN would have a big problem itself against them.
Japan isnt spending to protect herself. Japan is spending to give a credible deterrent with the knowledge the USA will be coming to the rescue. At least vis-a-vis the Chinese. And Im not sure the Chinese would automatically fire these IRBMs. Touching off missiles is risky business, most of all swarms of them, most of all when an opponent has a very large nuclear inventory herself. Far larger then they have. Not that America would push the button if we saw these things flying but you can be sure we'd be one step from doing so.
And launching these missiles, which have never even been tested against an actual ship, would open up the Chinese mainland to a concerted attack by smart munitions against high value targets.