Why build destroyers instead of torpedo-boat leaders?

Why did navies build destroyers rather than torpedo-boat leaders?

Early destroyers already acted as torpedo-boat leaders. Once destroyers became larger and more capable, adding another type between them and torpedo boats risked complicating the fleet without supplying a clear additional role.

The answer changes with the period under discussion. An early destroyer already performed much of a torpedo-boat leader's work, so a differently named type could duplicate its role. Once destroyers had developed further, a separate leader would insert another vessel between a destroyer and a torpedo boat. The comparison with a proposed medium cruiser explains the objection: an intermediate type can cost more than the smaller ship while remaining unable to perform the larger ship's work. Adding that category could complicate the fleet's organization without a distinct operational purpose.