Wait, what?
Let's do a quick review:
- 056 is 1400 tons full load, with 4 AShM, 1 76mm gun, 1x8 missile CIWS SAM, 2x30mm autocannon
- 054A is slightly over 4000 tons full load, with 32 VLS and 8 AShM, 1 76mm gun, 2x30mm CIWS
- 052C is estimated to be 7000 tons full load, with 48 VLS and 8 AShM, 1 100mm gun, 2x30mm CIWS
- 052D is estimated to be 7500-8000 tons full load with 64 VLS, 1 130mm gun, 1x30mm CIWS and 1x24 missile CIWS SAM
So if we compare each displacement class with its international peers:
- 056: The only similar ships in displacement to 056 is the Sigma class 9113, which features 8 AShMs, 1 76mm gun, 2x4 CIWS SAM, and 2x30mm autocannons -- and 9113 is actually 200 tons heavier than 056. Even the German K130 corvette is 1840 tons full displacement, so 400 tons heavier than the 056 and its "extra armament" relative to 056 is two 21 cell RAM launchers. The Russian Stereguschy class features more advanced CIWS, more AShM and VLS, a 100mm gun, but remember it is over 2000 tons full displacement.
- 054A: Surface combatants in the world which are 4000+ tons displacement include OHP, Formidable/La Fayette class, Talwar class. 054A compares favourably to all of them in armament. Yes, 054A's VLS is limited to HHQ-16 and VLASROC and are unable to quad pack SAMs like ESSM, but that's a limitation of its VLS rather than something we can attribute to the ship itself.
- 052C/D: the only modern ship classes that sits comfortably in this weight class would be Type 45 and Horizon (sovremenny can be included if you want, but it's far from a modern ship). Burkes and their derivatives are at least 1000 tons heavier, while Eurofrigates are up to 1000 tons lighter. And 052C/D again compare quite favourably to Type 45 and Horizon in armament as well. 052C has the same number of VLS and AShM total as Horizon, while Type 45 is equipped for but not with Harpoons. 052D of course has more VLS than the total VLS+AShM count for both Horizon and Type 45.
So really I'm not sure why you believe that PLAN ships have less armament than their counter parts of the same displacement. In fact PLAN surface combatants hold different displacement categories compared to the USN's major surface combatants. Their current destroyers are 7000-8000 ton full rather than 9000+ ton full for Burkes. Similarly, 056s are 1400 tons and 054As 4000+ tons which do not correspond with the LCS's full displacement of 3000 tons
And finally, like tphuang said, armament alone does not determine the combat capability of a ship. The quality of weapons, the sensors, and combat management system are all as important as the number of missiles or variety of CIWS which is carried.
For the same reasons cited why armaments are not the only things that matter is why I conclude the PLAN ships are relatively underarmed. Ships are not designed to be exact equivalents so designs have to be compared roughly "up" or "down", their performance will be affected by other factors in the navy they are serving with, as well as their mission and operational environment including likely opponents. So I will have to agree to disagree.