I have to admit I am out of date with Japan’s military. All I really remember was the grumbling of Japanese Neocons grumbling over Article 9.
China’s naval buildup seems to be directed towards this exact scenario. Do they have numerical superiority yet?
China has numerical superiority in a simple-minded “bean count” way, yes.
The same way Iraq had numerical superiority in troops, artillery pieces, etc. over the Coalition in Desert Storm.
The Chinese Navy is basically helpless at ASW; just the (very quiet and very deadly) submarines of the JMSDF alone could run riot sinking every Chinese vessel at sea, if they wanted to.
The Japanese are much better trained, and overall have a higher level of technology (especially proven technology.)
Not where it counts. Most of the PLAN ships are small fast attack craft which would be sitting ducks in the open ocean.
In Fleet units the PLAN and the JMSDF have 10 ships of DDG size 6000tn+) or larger - But a Kongo is qualitatively better than a Type52C.
Smaller DD/FF ships the PLAN has 63 - two thirds light frigates less than 3000 tons, the JMSDF 38 - but 83% over 3000tons.
Under the waves the PLAN may have numerical superiority with 40 SSN/SSK (up to 10 steamers) to the JMSDF 18 SSK but as Strategerist pointed out, the JMSDF has been practising ASW for the last 50 years, One presumes they are fairly good at it by now,