Ship designations are more based in function, than displacement. Frigates were traditionally designed to operate independently from fleets, where destroyers are generally escorts for fleet vessels, like transports, cruisers and carriers.
Cruisers were traditionally designed with specific missions in mind, air defence cruisers(Ticonderoga), anti-ship cruisers (Slava), etc
But cruisers are going out of fashion, with navy’s opting for more capable Frigates and Destroyers over time, which is why the displacement has been growing.
Ship designations are more based in function, than displacement. Frigates were traditionally designed to operate independently from fleets, where destroyers are generally escorts for fleet vessels, like transports, cruisers and carriers.
Cruisers were traditionally designed with specific missions in mind, air defence cruisers(Ticonderoga), anti-ship cruisers (Slava), etc
But cruisers are going out of fashion, with navy’s opting for more capable Frigates and Destroyers over time, which is why the displacement has been growing.
Even these generalities depend on the navy and on history. Sometimes even in the same navy there are back and forth with namings.
The short answer is always: “it depends” :)