I'm not yet sure if a two or three tier system is optimal (with the 13000t 055 family and the frigate both being two of the tiers) -- nor am I sure what displacement the frigate should be.
Personally. I feel like a 5000t frigate (with growth expansion to 5500t) could be a good middle ground -- for 054B.
Slotting between the 13000t and 5000t weight classes would be a 8000t true clean sheet successor to 052D.
==
The "delays" for 054B I suspect are a combination of introduction of new technologies to 054B from what they may have originally intended back in the late 2000s (assuming 054B would've already been being worked on back then given the build/develop/research a generation method the PLA uses), as well as requirement for more hulls in service that may have been deemed important sometime in the late 2010s deu to the changing strategic environment.
Agree.
My personal idea, albeit simpler, would be something like this - Categorization of surface combatants into light, medium and heavy classes for the Navy, which is somewhat akin to light, medium and heavy fighters in the Air Force.
Light surface combatants would be Frigates, i.e. Type 054As and (maybe clean sheet) Type 054Bs.
Medium surface combatants would be Destroyers, i.e. Type 052Ds and (maybe clean sheet) Type 052Es.
Heavy surface combatants would be Cruisers/Large Destroyers, i.e. Type 055s and (maybe clean sheet) Type 055Xs.
Corvettes don't count, since they aren't exactly meant for naval surface combats on the high seas, and are therefore focused more on coastal and near-coast operations.
This would be sufficient for a fundemental 3-tier surface combatant system for the PLA Navy, sufficient to address all kinds and magnitudes of threats in the naval domain.