You are right about the HQ10's multiple target engagement advantage, but it also compromises at range and warhead lethality. The 76A guns on older ships utilize double hit probability theory, using a combination of radio proximity HEFRAG shells at long range (3000m) and APFSDS at close range (<1000m), they are not completely useless against sea skimmers. Those ships are by no means better than 056 at air defense, but certainly not inferior.
I'd be very surprised if 056 carries reloading mechanism for the HQ10, it's designed to be a flexible system that maximizes on compatibility, which means no deck penetration. OTOH I think they have the capability to reload manually at sea, that's how USN reload their SeaRAMs.
BUt USN RAM are usually install on big ships which are less prone to high sea rocking. 056 is only 1300tons and North Sea and South China sea is by no means calm. Manual loading will be highly dangerous. I belive auto reloading mechanism for FL-3000N missile need not to be too big since the missile is not huge after all.