Gentleman, I think it's silly to make comparisons between China and neighboring countries in terms of tonnage or quantities. The fact of the matter is China will have any many cutters as it deem necessary in their operational and strategic planning and as budgeting allows. PERIOD!
To assume why China need X many ships when others doesn't or vis a vis Japan is like asking why the USCG is what it is when Canada and Mexico doesn't even have 1/25 of what the USCG does yet their coastlines are similarly huge as well!
Also by it's very nature a CG ship is not intended to confront an actual naval vessel in a conflict. Primary goal of the coast guard is mainly to safeguard a countries's coastline and EEZ, law enforcement, maritime security, rescue operations and thwarting criminal activities in the high seas!
A cutter no matter how big can't and won't be used to confront a submarine, destroyer, cruiser etc!!!! You don't need to load it up with crazy weaponry to fight off local pirates, drug runners or human smugglers etc.
If the day ever comes where CG vessels are the only ones left to fight off a destroyer, SSN etc guess what? the war is already lost!
Agreed. However, I believe one would also agree with this idea of a cutter... to let other nations know of the presence of whatever country that cutter belongs to. A cutter needed to be armed... maybe not to the standards of a Navy warship, but definitely needed to be armed decently, not just to confront local pirates, but also to show others that they means business. And I believe that is what many nations were doing with their cutters (eg. Japan).
China, on the other hand needed that too, so that she wouldn't need to keep falling back to her Navy ships when doing patrol in disputed sea and islands and needed confrontation with other nations' cutters. Without decent armament, she needed to call for assistance from the Navy and that would again give others an impression of the China threats.
If China's ships are decently armed (at least with a 76mm canon), then she wouldn't need to called back for assistance, she could definitely more effectively protected her assets in these islands, and to the outside world, China didn't send any Navy assets to 'press' down the other nations.
And having larger number of armed cutters are of vital importance, not because other nations have x number of similarly or heavier sized ships, but to ensure that there are enough to cover the massive coastline and more of China. When I said in comparison with neighbouring nations, I didn't mean because Japan, or South Korea or even the Phillippines had x number of ships then China must have x number of ships, I mean, taking example of Japan who have so many ships, why couldn't China also build the same number or more of ships without anyone coming in and claim China of being overkill... or again... China threat?