It seems HQ-011 doesn't have any air defence SAM ... it will be a sitting duck against Chinese PLAN in no time
That is not correct.
The anti-missile system aboard the two current Vietnamese Gephard frigates (HQ-011 and HQ-012) is the Russian Palma system, which it the export name for the Russian Kashtan system. You can see it installed there on the HQ-011 just aft of the main gun.
This is a very modern and very effective anti-air, anti-missile system. The two additional Gephard frigates that the Vietnamese are building will have the same.
Palma/Kashtan is a combination gun and missile system. The guns used are six-barrel 30 mm rotary cannons. Each of those guns (and there are two with each system) are the Russian GSh-30K. Each individual rotary cannon has a higher rate of fire than the GAU-8 on the Goalkeeper or the M61 Vulcan on the Phalanx. The round is also larger and heavier.
The air defense missiles that is used by the system are Russian 9M311 missiles. They are SACLOS guided missiles and are steered automatically by the command module. The warhead is a rod warhead with a steel cube fragmentation and is either laser or radio fused. Detonation creates a complete circle of fragmentation that is 5 meters in radius, exploding in front of the oncoming missile to destroy it.
The combination of the two (missiles and guns), provides a more comprehensive defense for the vessel, particularly when compared to single mode system, either guns alone, or missiles alone, for CIWS.
To say that these Vietnamese vessels do not have any SAM defense and would be a sitting duck against anti-shipping missiles is simply not correct.
Each gun has a range of up to 4,000 meters and a fire rate of 9,000 rounds per minute.
The missiles have a range of up to 10,000 meters and are all aspect at altitudes from wave skimming up to 20,000 feet.
The system carries eight missiles ready to fire, and these systems usually have an auto-loader with an additional 32 missiles stored below deck.
So, they have a very decent anti-air defense for such frigates. It is not an area defense, but very good for themselves.
Also, the Chinese Type 056 corvette uses an eight cell launcher for the FN-3000L system, which uses the surface to air verison of the TY-90 missile. The FN-3000L variant of the TY-90 missile is a very good close in defense missile similar to the US Rolling Air Frame Missile. It has a range of 9 km against sub-sonic missiles and 6 km against supersonic missiles.
So with 8 of those missiles with a range of 9 km max, and that being really the only decent anti-missile defense, compared to the Gephards 40 missiles with a 10km range, which are backed up by two 9,000 round perminute cannons for close in missile dfense, the Gephard is actually better armed than the Type 056 for anti-air defense.