Why are the sea trials taking so long? I mean, we basically have 3 type 052Ds in sea trial while only one in service....
052D 1 was commissioned early, but probably with less capabilities that could be considered fully operational, OTOH later commissioning of subsequent 052Ds may reflect that they are commissioned with more capabilities operational from the outset.
In other words, I think the actual commissioning date of PLAN ships isn't that important but rather it is how many capabilities the ship has at a particular time and how familiar it's crew is with their ship which is more important.
I also think that the fitting out process takes longer than the time it takes to fabricate and launch a new hull, meaning if production of units occur continuously like how we see at JN, then the shipyard may have to simultaneously fit out many ships at once, the more ships there are meaning a longer fitting out process for each ship as they're dividing their work force over more vessels. This means there will be a delay in commissioning ships early on but may reflect more rapid sea trials and commissioning at a later date.
Otherwise the alternative is to maintain the same work force to fit out each boat in a chronological basis which will probably leave the newer launched boats having to linger and wait for work to even begin. The solution should be to train more work force, but that has its limits as well.