But alas my friends. Recall that Romulus no longer exists. While the Romulan Star Empire has potentially hundreds of conquered worlds and potential colonies where Romulans might still exist. I doubt they will seriously involve themselves in conflict of that magnitude with their races being nearly extinct.
If we decide to ignore JJTrek's meddling with the Prime timeline. We have to look at the dreadnought class Scimitar ships. With their extreme armaments, perfect cloak that can be activated while disruptors and torpedoes are fires, enhanced shields, and the planet encompassing thalaron weapon. If the Romulans were involved in another Dominion War the Federation would be hard pressed to prevent them from using that bio weapon. Hell a fleet of Scimitar class ships would be enough to cut Jem'Hadar and Cardassian ranks to pieces.
With Starfleet we had to remember that they are not a military per se. The Klingon and Romulan fleets are militaries. Romulan's making advances in military might is to be expected. While Klingons are routinely shown to be apemen with rockstar hair. Military ingenuity seems to have left them after TUC. Since the Klingons were the first to develop a ship that can fire while cloaked. The Federation has developed phasing cloaking technology but it was in violation of a treaty with the Rommies. However the tactical advantages of a phasing cloak can't be ignored in an all out war.