Romulans did nothing more on DS9 than they did on TNG, TOS or ENT.
Klingons were stupid gorillamen and drunks mostly. Even Kor who was serious and militant became a trope. Gowron who had intellect and courage in TNG became a spoiled and incompetent character for the sake of conflict on DS9 leading up to the Dominion War, and died a trope.
Cardassians were little more than epic trolls to the DS9 crew prior to the Dominion War. Always finding some way to fuck with our heroes every other week as if they didn't have a government to run.
The Bajorans preachy religiousness was pushed to much and to far in the viewers face. They were annoying, bratty and thought the universe revolved around them. TOS, and TNG showed us the universe is full of different species every week. DS9 camped down and we actually got to learn about one. I personally couldnt care less about the Bajorans.
Also it was Gene's rule since TOS that conflict show come from outside the ship. Sure every series has it's tiff's but never do we see a crew engage in open hostilities like mortal adversaries. These are trained professionals doing a job in deep space, on stations and ships. Not sports teams with competing records and ego of each player. All one has to do is look up Harlan Ellison and his controversy with Gene over "The City On The Edge Of Forever", and immature it is to insert faux drama in between the crews of ship. Not saying you can't write drama but don't be lazy about it. You'll find yourself taking the easy road out like VOY did with the Maqui.