I'm assuming that you are referring to a lack of a playable Destroyer; fact is DW shipped with what the Developer's intended it to ship with. We can't simply have everything we want. This question has cropped up many times, truth is that Sonalyst control what is playable and only through our continuted support as a consumer base will ensure future expanison(s).
So basically they could claim that yes DD's/DDG's are redundant to the FFG we already have and would not further enhance the game experience.
I'm hoping that Dangerous Waters is another stepping stone for Sonalysts and we will continue to see the product evolve from greatest naval sim to "uber" sim.
688i > Planned Aegis DDG Sim > Fleet Command > Sub Command > Dangerous Waters > "Greatest Naval Simulation of all time"
the above is mostly my view so just take it with lots of beer