Edit, i dont think cost acts as an effective way of defining a unit. We've got 2 closely statted units but with distinct roles within a build. One that'll pair with the slower gustav's and another that'll dash for objectives.
I tend to think of units by cost because for BBs cost has often been determinative (a 40 point BB usually can't handle a 50 point BB, etc.). On top of that; I like the idea of abilities filing out consecutive price differences in a given class or type, though with DDs this is not quite possible, and DDs also vary more in the roles available to them than the heavier types of ships.
Despite all of that, I am inclined to agree with your reasoning though; two different roles should be enough to distinguish the pair of dds.
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