Klingons, on the other hand, just go in and conquer or blast the shit out of you, so "Battle Cruiser" seemed more appropriate.
To be sure, Klingon ships in TOS always played sneaky and dirty tricks. There was no "simple blasting" in any of the episodes, really.
In "Errand of Mercy", our introduction to the Klingon species sounds very much like an attack by a cloak-capable Bird of Prey: an enemy appears from nowhere, completely surprises our heroes despite them being on war alert, and launches a volley of torpedoes which all score perfect hits. The Enterprise
shrugs off the hits, responds with a phaser blast, and the enemy is immediately dust.
Whenever Klingon Warbirds (sorry, battle cruisers) confront our heroes, they either yield ("Trouble with Tribbles", TOS-R "Friday's Child", "Time Trap"), or rely on saboteurs ("Elaan of Troyius") or strange superweapons ("More Tribbles, More Troubles") or superior numbers (TOS-R "Errand of Mercy", STXI simulation). Gorkon's flagship in ST6 is a rare exception to the rule, a bravely acting single Warbird...
Klingon ships also all tend to look like birds (wings, neck, head), while the original Romulan one did not.