Speaking of Cloaks, why did the Defiant have a Romulan cloaking device, rather than Klingon?
I think the reason is more easily explain diplomatically then technologically.
To the best of my knowledge, we never get any true insight into who has a better cloak (Romulans or Klingons) though I think we could probably make a good argument for Romulans having a better cloak considering they are more interested in technological advancement then Klingons.
However, the explanation, IMHO can be found in the TNG episodes: "The Pegasus". Based on that episode, the Treaty of Algeron
expressly forbids the federation from developing or having cloaking technology and therefor they need permission from the Romula Empire to use it. In order to properly oversee that they aren't misusing it, doesn't it make the most sense for the Romulans to give them a cloak?
As for "Why no Romulan Ships?" I think Dub's answer would be the one used, but frankly, I think the big explanation would frankly have been budget.
Let's be honest, budget not being a concerned, we'd expect to see about a dozen ships around the station at any time, not one or two.