The problem is that there are two competing modes, and the roles are evolving to fit, in ship design:
Multi-mission and Single-mission.
Multi-mission craft are designed either for the ability to fill several roles in a fleet structure.
Singlemission focus on one mission to the exclusion of others.
Cruisers had range, originally, on heavy frigates and light Ships of the Line, hence the name.
They gave up armament for range, and once armor became common, single-mission ships could easily outdo them on any one area.
Battlecruisers sacrificed some fo the range (1880-WWII) for larger guns and more armor, plus generally were less equipped for the non-combat roles.
Pocket Battleships sacrificed even more range for the heaviest armor and weapons they could mount on the hull.
Corvettes are small, fast frigates.
Traveller generally uses the term destroyer for the Frigate role: the smallest ship of the line, and the basis for the secondary lines. (hence being the smallest classes routinely mounting spinals.)
Just for the historical basis, from Wooden Ships and Iron Men:
Class 1 and 2: Ships of the Line
Class 3: Frigates
Class 4: frigates and corvettes
Class 5: sloop, schooner and brig
Class 6: Gondola, Galley, and Radeau
Class 7: Gunboats
This was a typical understanding (and IIRC, is based upon the fench method of classes from the time).
Destroyer is a WWII term, as destroyers were pack-oriented, and often operated in independant packs, ratehr than as integral parts of larger fleets... at least in theory.
Pocket battleship is a term applied to certain superheavy cruisers (Several arms limitation treaties defined Cruisers by displacement... and the germans and brittish promptly built ships right to those limits, and some were shorter ranged so they could mount armaments expected of Dreadnoughts and Battleships.
Think of a PBB as being , in Traveller HG terms, an AV10+ heavy cruiser, mounting an ABSOLUTELY HUGE armament Spinals R+, multipel hundred ton bays.. but having only J3, not the typical J5 of fleet units. Battleship armaments, cruiser hull, and from a distance, not being THAT threatening...
Historically, HMS Dreadnought, being one of the earliest Battleships, was also one of the smallest....