Why warship designs cluster around recurring displacement bands

Do warships have similar sweet spots and bad spots in displacement?

Yes; once a navy defines the mission, the required capabilities tend to pull the design toward recurring size bands.

Displacement follows the mission and the capabilities a navy wants to fit into a ship. Similar requirements repeatedly lead designers toward familiar sizes. Some displacement bands consequently suit a set of requirements better than neighboring sizes. The relationship is qualitative, with no numerical bands or displacement formula specified.