CEC can work across ships with differing families of sensors, for example, Wasp class and Nimitz class to AEGIS Burke.
The problem of the 054A, is that it uses sensors that operates in a way that is so completely different from the 052C/D. It feels like the 054A doesn't belong to the same country, or the same decade. Their weapons systems are not even compatible. That will not stop a 054A from operating in a CEC environment with a 052C/D or 056A with the proper datalink and combat management software.
But the strain comes from logistics and training. The HQ-16 does not operate like the HQ-9, whereas most ships in the West, US allies included, use the Standard family, and the ESSM that works the same like it in guidance principle and system. If you put an HQ-16 on a 052C/D, it won't work. If you put an HQ-9 on a 054A even if you put a U-VLS on it, it won't work.
The problem in the long run is that it is difficult to invest long term development projects on two different SAM and VLS systems where you should only be investing in one. If you improve on the HQ-9 it means zilch benefit for the 054A. If you improve on the HQ-16, it means zilch benefit for the 052C/D.
If I were to develop, let's say a quad pack MRSAM for the U-VLS, it will only work on the 052D, but not on the 054A. Our new hypothetical SAM may end up fitting on the 054A's VLS on a one to one basis only. If you develop a quad pack SAM for the 054A's VLS, such a SAM might end up a bit small and under performing. It appears the H/AJK-16 and the HQ-16 system is going to be a technological dead end.
While the 054A has surprisingly large amount of sensors --- five different sets of radars and emitters --- without counting navigation radars --- they are also dated, with European frigates (at a great financial cost) going into AESA since the early 2000s. Now there are also cheaper frigates that are going solid state, like the Italian PPA and the French FTI. The problem of older, mechanical sensors is their "noise" --- their radar emissions coming from their sidelobes can be picked up by ESM, and lets you geolocate the ship for targeting. Older sensors may also not be as agile in dealing with modern ECM. Older sensors may not be as good in detecting and locking on to stealthier threats in time.
The 054A maybe good in handling threats circa 2000, and still good around 2010, but 2020 is probably where it ends as new weapons like the LRSAM are coming, and has no role by 2030 other than being a target. So these ships, around 30 of them, is going to need a hefty midlife update program to happen even if the ships are still young.
IMO this still doesn't answer the question as to whether the 054A was a sensible procurement choice with the production run that it had.
Considering that the PLAN is still actively upgrading legacy ships like Sovs and more recently the 051B with a similar sensor and weapons suite to what the 054As have, suggests to me that they are comfortable having such a system in service for the next 10 years or so. As second line surface combatants, I believe the capability they offer is quite adequate.
For 054As, it is certainly reasonable to expect them to get an MLU in the future, perhaps starting in the mid 2020s for the earliest boats. In fact I would be surprised if they didn't receive an MLU during their service life.
But the way you write about 054A, makes it seem like you think 054A should have developed a more advanced variant with more capable sensors (AESAs, more integrated electronics etc) partway through its 30 ship run.
I think you are both overestimating the PLAN's expectations for 054A, as well as forgetting how recent it was that the PLAN had started building 052C/Ds and 055s in large numbers.
Compared to 052C/D, the 054A was a much more medium tier, medium technology, medium capability surface combatant. Its primary combat systems were not even cutting edge for the PLAN when the class was first introduced (i.e.: 052C emerged around the same time as 054A did).
052C/D production began in earnest around 2010, and then 055 production began around 2015-2016 as well, and these were two concurrent classes of advanced, large AESA toting warships carrying the fruits of the PLAN's R&D and combat system development over the prior decade or more.
I question whether it would have been wise for the PLAN to stop 054A production to move onto an improved frigate with the capabilities you're talking about during this exact time period, given the profile 054A was meant to have in the PLAN's overall force structure, as well as the other surface combatant programmes the PLAN had going on at this time.
OTOH, I can very much see the argument for having an improved frigate (whether it's called 054B or 057 or whatever) enter service in the early 2020s, featuring similar technologies and systems to what 055 had -- but by the time 054B/057 enters service those technologies and systems will be mature and cheap. It is also likely that 054B/057 may introduce one or two new key technologies to their class (such as IEPS), but it will still overall be much lower risk as it will be porting over technologies and systems that are mature when it enters service.