The Romulans were originally a minor power, behind the Federation's advances since being defeated and isolated after the Romulan war. In their first appearence ("Balance of Terror"), they had a ripped-off Starfleet ship with a bird painted on it and no warp drive. It was only their new cloaking device and plasma torpedo weapon that made them formiddable. Later they got better, Klingon-designed ships.
Later Treks, most notably Enterprise, would retcon Romulans into a big galactic power in the 22nd and 24th centuries, with warp drive and cloaking devices, holographic starships and a vampiric slave race.
As for the Klingons, they were originally the Soviet Union to the Federation's USA. Other Treks would turn them into an almost technologically stagnant society, using the same ships in Enterprise as they do in DS9, 225 years later. On par with the Federation in TOS, far above them in ENT and lagging behind in DS9. Since reading the novel Ishmael
years ago, I like to think Klingon technology is inhereted from their former slave masters (the Karsid Empire), who mysteriously vanished 600 years prior to TOS. It explains why all their ships are old rustbuckets.