I would argue that fewer Romulans died because they joined the war effort.
Or, it's possible that Romulus would have just surrendered once they were surrounded by the Dominion. But centuries of slavery isn't much better than death.
What Sisko did is very debatably the right thing to do, but it has nothing to do with Star Trek morality. It's an outright critique of Star Trek morality.
It's entirely possible that the average citizen wouldn't even have noticed a difference. Pay your bills, do exactly what they say, and the Dominion won't send in the Jem'Hadar.
The Founders goals are not to be evil overlords, but to bring order from chaos and to set up mechanisms to protect themselves from solids.
The real problem for the Klingons and Feds if they lose the war (other than that whole 'let's wipe out Earth's population' thing) is they are going to be the CARDASSIANS and BREEN's subjects. *That* is going to suck.
Now Romulus does have the problem that they tried to wipe the Founders out (even though they were manipulated into doing so.)