If you look at Chinese military doctrine of "winning localized war under the condition of informationalization," type 054A fits perfectly for such role in China's periphery. Most of the type 052C/D, 055, nuclear-powered hunter subs, and carriers are for future engagements in places like the Malacca Straight or the Indian Ocean, where Allied (and India) forces could easily cut off China's maritime oil/gas supply routes. For China's periphery, you just need a massive number of type 054A, 022 missile boats, and 056s corvettes supported by land-based/air-launched long-range AshMs for defense against Allied "Air-Sea" battle concept.
I think you're making a mistake, in that you're assuming all larger, longer endurance ships will be used for blue water operations whereas smaller, shorter endurance ships will be delegated to operations in the western pacific.
The truth is, if PLAN ever fights a war in the western pacific, they will want to bring everything they have into it, especially if it is against a peer rival like USN or JMSDF or both. They won't only be relying on 054As, 022s and 056s. They'll be bringing in 052C/Ds, 055s, carriers, LHAs, LPDs, SSNs and SSKs. They'll want everything there including the kitchen sink.
Sure, in theory 055, 052C/D, and carriers, etc, are meant to defend China's SLOCs and trade routes at sea, but realisticaslly, it'll be many decades until China can fight a high intensity global naval war against a peer opponent like the USN. In other words, the PLAN would be suicidal to send a CSG out into the Indian ocean against a USN taskfroce out there. The only viable way for the PLAN to fight the USN is to fight in the western pacific where China can rely on land based missiles and airpower and C4ISR to even out the odds.
In reality, I expect future PLAN CSGs in the Indian Ocean and around Africa to mostly serve as force for lower intensity operations and to defend against second tier navies that could threaten Chinese shipping. Against a first tier navy like the USN, a PLAN CSG would have no chance without the benefits of land based airpower and missiles.
As for "winning localized war under the condition of informationalization" -- there is nothing about 054A that makes it better suited to that than any other modern PLAN surface combatant. That kind of doctrine is basically advocating network centric warfare near China's borders, and in terms of maritime borders that extends to and beyond the first island chain. There is nothing stopping 052C/Ds, 055s, and carriers from operating in that area, and there is nothing that makes 054A better suited to it. Besides, what you're saying makes it sound like the PLAN is safe just using 054As, 056s, 022s and land based missiles to fight in all localized maritime wars -- including situations involving the USN or JMSDF? Hell, even in a conflict against a lower tier navy like Vietnam's, I would still feel safer if I had some destroyers and a carrier in the mix.
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And this goes back to what you said about 054A's mostly being useful for anti piracy and patrolling the SCS. Which I disagree with. For one, 054As have not patrolled SCS like Tphuang said.
But more importantly, 054As are useful in virtually any situation. They are small and flexible and cheap enough to be used in anti piracy roles, but they're armed well enough to contribute to a larger task force like a CSG or ESG. They also have enough range to do blue water missions. Sure, you need more meat in your navy's orbat if you want to put forward a more serious CSG or ESG, in which case you need 052C/Ds and 055s. But that doesn't mean 054As aren't useful. In fact I'd say they are quite important. They help build up the numbers in your taskfroce, they are small and cheap enough to play tag with submarines in ASW roles, and they have the radar and SAMs to network with the overall air defence situation.
In other words, 054A is a good multipurpose, modern frigate that can be used in a variety of low and high intensity situations at long range or endurance, that can be mass produced with good capability for how much it costs. That is why so many have been produced. It isn't because the PLAN thinks 054As will only be good for SCS patrols or anti piracy or that 054As will make up the main meat in their naval taskforce if they fight a westpac war.