Wasn't the Romulan Bird of Prey originally meant to be a salvaged or ripped-off Earth design from the Romulan War era? That and the "simple impulse" drive makes it pretty clear that they were in dire need of modern vessels (at least in the pre-retcons TOS universe)
It’s my understanding that based on the initial script, the Romulans stole Starfleet designs, and the BoP was supposed to resemble the Enterprise’s saucer section. Since it had no warp nacelles, it would have only had impulse drive (hence Scotty’s comment about simple impulse.)