You're right about electronics warfare factor. SAMs surely would have AAMs beat if they are given the same effort to maximise ECM ECCM.
The cost and production rate factor is definitely there but I still think the HQ-16 can do with a modern replacement that improve speed and range without sacrificing warhead and electronics. For one thing, two stage SAM is more kinematically optimised than something like HQ-16 which has to drag the entire massive frame around when fuel is depleted.
With repurposed AAMs to SAMs, at least the packing is going to be dramatically improved. If a new SAM is developed to be quadpacked onto VLS on ships or vehicles mounting 12 missiles instead of 6, it will suffer from the same issues as the repurposed AAM because it'll be about as thin and demand the same miniaturisation of component along with the same complexity and cost. The difference is those AAMs are already developed and just require some fine tuning and a booster stage. DK-10 is rated at 50km for export. A PL-15 based SAM for PLA with booster stage based on available rocket and fuel tech now, should clear 100km. That's still better range than HQ-16 and better speed.
So it comes down to cons being extra cost, fewer total missiles, weaker or similar ECM ECCM. Advantages; better kinematic performance, more missiles per launch vehicle/VLS, slightly longer range.
I just wish the HQ-16 could ditch a booster stage to improve performance instead of dragging around dead weight. Would make it around mach 4 capable, retain energy for turns and be much harder to defeat by a fighter.
HQ-16 is about the size and weight of RIM-66 Standard give or take 690kg or 715kg vs. 707kg. There is nothing massive about it --- it is a medium sized missile after all, not big, not small, certainly not massive. At only over 5 meters in length it would be undersized on let's say, a 7 meter deep U-VLS cell.
Also the speed can still be boosted like what happened to the 9M317ME variant here. HQ-16B is similar to the 9M317 Buk variant.
Note that it says 960 meters per second for average speed or Mach 2.7, but maximum speed is about 1550 meters per second or Mach 4.5. The average speed is probably for a longer ranged cruise mode wile the maximum speed is for a fast sprint on closer ranges.
While there is little detail about the seeker of the HQ-16, which is likely
not the same as the Buk's, the Buk's seeker seems related or might be the same seeker used on the R-27 air to air missile, which is a fox 1. AGAT however offered using an active seeker, based on the R-77's, as a replacement upgrade of the seekers, but it doesn't appear this was concluded. However it does tell you that the potential is there to replace the seeker to an active one, and there is the same potential for the HQ-16 seeker to move to another seeker, like the PL-12's or the PL-15's. Possibly even the HQ-9's. If the missile is active seeking, it can likely boost the range, as the missile range is currently limited by the range of the target illuminating radar, and the active seeker makes the missile independent of such a device.
This picture below shows a proposed refit of the Russian owned Sovremenny similar to the PLAN with the VLS installed at that position. The difference of the Russian VLS for the Shtil is that it is cold launched and not hot launched like the HHQ-16.
It is interesting to note that the missiles have a service life of 15 years, which means that the missiles used for the two earlier Sovremennys and the 052Bs would have been shortly expired by now, and that would justify the refit of these ships to the domestic HQ-16. The last two Sovremennys are newer and still good but they should be in for a change in the next few years.
