Have we forgotten the idea of peacetime and wartime ratings, then?
As I recall it, one relatively easy way out of the confusion was to assume that a lot of it existed in universe. The Bureau of Ships and Services maintained a system that was very bureaucratic and hidebound, and reacted to galactic change very slowly; what they called a ship, what the press called a ship, what the manufacturers called it and what the end users called it could be four completely different things.
Broadly speaking the confusion resolves itself down into what the average being in the cantina says when he looks up at one of these things, and what the fleet says about it. Han is an outlier- he's Corellian, and the Corellian Navy tended to the light fast and numerous, attack boat tactics, so by his standards it probably was a cruiser.
To blow my own trumpet here, some time ago I tried to tie it all together and came up with this as the Starfleet version of the classification ladder;
Dreadnoughts; Mandator- I, Mandator-II, Executor, Sovereign, Eclipse
Battleships; Giel’s Star Battleship (“Prolocutor”?), Anon battleship II “Defensor”, III “Conducor”, IV (still thinking about names)
Anon (“Aquila”?)Star Carrier
Battlecruisers; Vengeance, Procurator, Praetor, Ultor (?)/Tagge’s, Wermis’s/(“Adversor”)
Cruisers; Anon- I “City”, Anon-III “Senator”, Anon-II “Admiral”, Anon- IV “Starburst”, Anon-V “Sector” classes
Heavy Destroyers; Invincible, Allegiance, Anon SD VII “Ordinator”, Anon SD III “Proelium”, Shockwave
Line Destroyers; Tector, Imperator-I, Imperator-II, Anon Interdictor SD “Dictator”, Dominator, Anon SD IV “Retexor”
Light Destroyers; Venator, Anon SD II “Arrogant”, Anon SD VI “Spoliator”, Karu, Harrow/ “Excrucior”, Victory-I, Victory-II, Anon SD I “Victory-III”
Heavy Frigates; Acclamator, Ecliptic, “Meridian”/Acclamator-II, Vindicator
Medium Frigates; Centax, Demolisher, “Pabulator”/Neutron Star, Broadside, “Verberor”/Strike, Dreadnaught
Light Frigates; Fulgor, Interdictor, CC-2200 Detainer, “Comitor”/Escort Carrier, Anon Prison ship II “Moderator”
Heavy Corvettes; Anon prison ship I “Quaestor”, Anon Corvette II “Servator”, class 1000, Carrack
Medium Corvettes; Bayonet, Anon Corvette I “Vagor”, Anon Star Monitor “Oppugnator”, Nebulon B, Nebulon B2
Light Corvettes; Marauder, DP20 Corellian Gunship, CR90 Corellian Corvette, Assassin mod corvette, Lancer, Prosperity “Praecurror”, Rendili Light Corvette
It was a long time ago and there may be a couple of things needing filled in, but you get the idea- there is a long continuum of warship types that Imperator/Imperial- class end up pretty much in the middle of. (Incidentally, I agree with the idea that there simply isn't enough variety around, but convergent evolution of designs might squash some of that anyway- a good design for a job is a good design for a job, they all tend to end up looking alike. That and local license building of proven types. And what a headache for the special effects crew.)
That does make them the median swing types, small enough to escort large ships and large enough to dominate enemy small ships, maids of all work for the fleet. Which is not far off the modern definition of a destroyer, actually.
Although I am unconvinced too of it's absolute meaningfulness, given the whole flight, helicopter, sea subsurface and air thing modern naval warfare has going on. (Translation; too many fators of nonsimilarity, too many separate dimensions of threat and purpose.) At most we're borrowing the names as indicators of relative weight and throw-weight, which is just as well because the suggestion of meaning they carry is more dramatic, more story-worthy, to me than something more technically accurate than the cold war russian navy's alphabet soup- RKRs and BPKs and PLARBs and all sorts. If a good story can be written entirely in pentagonese, go for it.
The universe- internal evidence does suggest that they sit essentially at that median point, with enough layers above and below to fit the destroyer role- as well as presumably being titled something in Basic that translates to we the audience as Destroyer, of course. General purpose medium multirole, light and flexible enough to be used as the upper, reaction element in space control, heavy enough to be meaningfully useful in major engagement. What else would you call that?