However there are kind of ludicrous things going on when it comes to the use of "starship" and warp drives. "Starship" seems to be something grand by the way it is used in Kirk's time. Yet there has been warp capable ships before this, and ships that have warp drive that are not called starships. Merik's vessel for one. So "starship" was something special back then. Maybe due to the ship's size, or make just its high warp speeds compared to the older Warp 5 or even Warp 7 ships from the last century. USS Enterprise being at least a Warp 8 ship, as that was where Scotty started getting uncomfortable. But it could push it, and was able to get to Warp 14.1 at least for a movement on its own power. Thus she probably has a Warp 10 engine like the NX-class has a Warp 5 engine, but rarely could got up to Warp 5.
The other ludicrous thing is the idea that the Romulans did not have faster-than-light drives in the 2260s. That makes absolutely no sense in context to everything we know about them even in the episode. We know that Earth fought a war with Romulus around a hundred years prior to the episode. There were lots of casualties and the weapons were relatively primitive (compared to USS Enterprise). Now, how would the Romulans and humans have fought a war in the Romulans did not have faster-than-light drives? If the humans found Romulus and the Romulans decided to fight them off, the humans could just as easily warp out and leave. No reason for a neutral zone, no observation stations of anything. Because were are they going to go? At sublight speeds it would take years to get to the nearest star system, and probably centuries or more to get to Earth. You can't fight an interstellar war effectively without faster than light drives. Even the long lived Romulans and Vulcans would require generational ships to fight a war. They aren't a threat, just leave them alone.
But if they have faster-than-light drives, than not only are they a threat, but they can get to Earth held space and fight an interstellar war. So that Bird of Prey had to have had a faster-than-light drive of some sort. Maybe not a warp drive, but something. Though it may not have been viable with the cloaking device on due to the power needed to stay cloaked, or a known problem with being detectable at ftl speeds while cloaked.
The other ludicrous thing is the idea that the Romulans did not have faster-than-light drives in the 2260s. That makes absolutely no sense in context to everything we know about them even in the episode. We know that Earth fought a war with Romulus around a hundred years prior to the episode. There were lots of casualties and the weapons were relatively primitive (compared to USS Enterprise). Now, how would the Romulans and humans have fought a war in the Romulans did not have faster-than-light drives? If the humans found Romulus and the Romulans decided to fight them off, the humans could just as easily warp out and leave. No reason for a neutral zone, no observation stations of anything. Because were are they going to go? At sublight speeds it would take years to get to the nearest star system, and probably centuries or more to get to Earth. You can't fight an interstellar war effectively without faster than light drives. Even the long lived Romulans and Vulcans would require generational ships to fight a war. They aren't a threat, just leave them alone.
But if they have faster-than-light drives, than not only are they a threat, but they can get to Earth held space and fight an interstellar war. So that Bird of Prey had to have had a faster-than-light drive of some sort. Maybe not a warp drive, but something. Though it may not have been viable with the cloaking device on due to the power needed to stay cloaked, or a known problem with being detectable at ftl speeds while cloaked.