Actually, the distinction between frigates and destroyers is
very blurred nowadays as both type of vessels have overlapping
roles(AAW, ASW), the only difference being in displacement(actually
some larger frigates have about the same displacement as a normal
destroyer).Put it this way,our formidable class frigates can
actually be considered as a"mini destroyer" itself.Therefore i
don't see having destroyer as very feasible, both in terms of
manpower and operational costs.
Just my two cents